-
[show abstract]
[hide abstract]
ABSTRACT: Glutamate extracellular accumulation is an early event in brain ischemia triggering excitotoxic neuron damage. We have investigated how to control the glutamate efflux from human cerebrocortical slices superfused in conditions simulating an acute ischemic insult (oxygen and glucose deprivation). The efflux of previously accumulated [3H]D-aspartate or endogenous glutamate increased starting 18 min after exposure to ischemia and returned almost to basal values in 6 min reperfusion with standard medium. Superfusion with Ca2+-free, EGTA (0.5 mM)-containing medium or with medium containing tetrodotoxin (TTX; 0.5 microM) inhibited the ischemia (24 min)-evoked [3H]D-aspartate efflux by about 50% and 65%, respectively. The ischemia (24 or 36 min)-evoked efflux of [3H]D-aspartate or endogenous glutamate was reduced at least 40% by the adenosine A(2A) receptor antagonist SCH 58261 (1 microM); the compound was effective when added up to 15 min after exposure to ischemia. No effect of SCH 58261 on the ischemia-evoked [3H]D-aspartate was found in Ca2+-free, EGTA-containing medium. To conclude, a significant component of the ischemia-evoked glutamate efflux in human cerebrocortical slices seems to occur by a vesicular-like mechanism. Endogenously released adenosine is likely to activate A(2A) receptors that enhance vesicular-like glutamate release during ischemia; A(2A) receptor antagonists would deserve consideration for their neuroprotective potential.
Neuropharmacology 12/2004; 47(6):884-91. · 4.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Adenosine released during cerebral ischemia is considered to act as a neuroprotectant, possibly through the inhibition of glutamate release. The involvement of A(1) and A(2A) receptors in the control of the rise of extracellular glutamate during ischemia was investigated by monitoring the effects of selective A(1) and A(2A) receptor antagonists on ischemia-evoked glutamate release in rat cerebrocortical slices.Slices were superfused with oxygen- and glucose-deprived medium and [(3)H]D-aspartate or endogenous glutamate was measured in the superfusate fractions. Withdrawal of Ca(2+) ions or addition of tetrodotoxin more than halved the ischemia-evoked efflux of [(3)H]D-aspartate or glutamate, compatible with a vesicular-like release. The glutamate transporter inhibitor DL-TBOA prevented the ischemia-evoked efflux of [(3)H]D-aspartate by about 40%, indicating a carrier-mediated efflux. The ischemia-evoked efflux of [(3)H]D-aspartate or glutamate was increased by the A(1) receptor antagonist DPCPX. The A(2A) antagonist SCH 58261 decreased [(3)H]D-aspartate or endogenous glutamate efflux (50 and 55% maximal inhibitions; EC(50): 14.9 and 7.6 nM, respectively); the drug was effective also if added during ischemia. No effect of either the A(1) or the A(2A) receptor antagonist was found on the ischemia-evoked efflux of [(3)H]D-aspartate in Ca(2+)-free medium. Our data suggest that adenosine released during cerebral ischemia can activate inhibitory A(1) and stimulatory A(2A) receptors that down- or up-regulate the vesicular-like component of glutamate release.
Neuropharmacology 09/2003; 45(2):201-10. · 4.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Presynaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/kainate receptors mediating hippocampal [(3)H]noradrenaline or [(3)H]serotonin release, striatal [(3)H]dopamine release and cortical [(3)H]acetylcholine release were pharmacologically characterized using several AMPA/kainate receptor antagonists. The releases of the four transmitters elicited by exposing synaptosomes to AMPA were antagonized by NBQX, indicating that they reflect AMPA/kainate receptor activation. GYKI52466 did not inhibit the AMPA-induced release of [(3)H]noradrenaline, [(3)H]dopamine or [(3)H]serotonin, while it weakly affected the AMPA-mediated release of [(3)H]acetylcholine. On the contrary, LY300164 and LY303070 were potent antagonists able to discriminate among AMPA/kainate receptor subtypes. Both compounds blocked the AMPA receptors mediating [(3)H]dopamine and [(3)H]acetylcholine release. However, LY303070, but not LY300164, inhibited the AMPA-induced release of [(3)H]noradrenaline, while the AMPA-mediated [(3)H]serotonin release was sensitive to LY300164 but not to LY303070. SYM2206 mimicked LY300164 and prevented the AMPA-induced release of [(3)H]dopamine, [(3)H]acetylcholine and [(3)H]serotonin, but not that of [(3)H]noradrenaline. NS102 failed to antagonize the AMPA-induced release of all four transmitters. LY293558 prevented the AMPA-mediated release of [(3)H]noradrenaline, [(3)H]dopamine, [(3)H]acetylcholine or [(3)H]serotonin. Differently, LY377770 did not inhibit the AMPA-mediated release of [(3)H]noradrenaline and [(3)H]acetylcholine, but it potently blocked the AMPA-induced release of [(3)H]serotonin and, less so, of [(3)H]dopamine. AMOA inhibited the AMPA-induced release of [(3)H]serotonin or [(3)H]acetylcholine, but not that of [(3)H]noradrenaline or [(3)H]dopamine. GAMS prevented the AMPA-mediated release of [(3)H]acetylcholine and, more weakly, that of [(3)H]dopamine, but it failed to inhibit the release of [(3)H]noradrenaline or [(3)H]serotonin elicited by AMPA. gamma-DGG did not affect the AMPA-mediated release of any of the four transmitters studied. In conclusion, based on the antagonist profiles obtained, the four receptors here analyzed all belong to the AMPA-preferring subclass of glutamate receptors; however, they appear to differ from each other, probably due to differences in subunit composition. The compounds LY300164, LY303070, LY377770, AMOA and GAMS may be useful to discriminate among AMPA-preferring receptor subtypes.
Neurochemistry International 04/2003; 42(4):283-92. · 2.86 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 1. The effects of adenosine A2A and A1 receptor activation on the release of glutamate were studied in rat cerebral cortex synaptosomes exposed in superfusion to adenosine receptor ligands. 2. Adenosine (0.1 microM) produced a significant potentiation of the Ca2+-dependent K+ (15 mM)-evoked [3H]-D-aspartate overflow (20.4+/-3.5%), which was blocked by A2A blocker SCH58261 (0.1 microM). At higher concentrations (10 - 1000 microM) adenosine inhibited in a DPCPX-sensitive manner the Ca2+-dependent K+-evoked [3H]-D-aspartate overflow. The inhibitory effect of adenosine at 1000 microM was significantly increased by SCH58261. This inhibition was antagonized by 1 microM DPCPX. Adenosine did not produce any effect on basal release. 3. The A2A receptor agonist CGS 21680 was ineffective on basal release, but stimulated the Ca2+-dependent K+-evoked overflow of [3H]-D-aspartate (EC50 approximately 1 pM). The effect of 0.01 nM CGS 21680 was totally sensitive to the A2A receptor antagonist SCH58261 (IC50 approximately 5 nM). 4. The A1 receptor agonist CCPA inhibited the Ca2+-dependent K+-evoked [3H]-D-aspartate overflow (EC50 approximately 20 nM). The effect of 100 nM CCPA was abolished by 100 nM of the A1 receptor antagonist DPCPX. 5. The K+ (15 mM)-evoked overflow of endogenous glutamate was enhanced by CGS 21680 (0.01 nM) and inhibited by CCPA (0.1 microM). The effect of CGS 21680 was abolished by SCH58261 (0.1 microM) and that of CCPA by DPCPX (0.1 microM). 6. It is concluded that adenosine and adenosine receptor agonists modulate glutamate release by activating inhibitory A1 and excitatory A2A receptors present on glutamatergic terminals of the rat cerebral cortex.
British Journal of Pharmacology 07/2002; 136(3):434-40. · 4.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: N-methyl-D-aspartate (NMDA) receptors exist on noradrenergic axon terminals and mediate enhancement of noradrenaline (NA) release. We here investigated modulation by somatostatin (SRIF, somatotropin release inhibiting factor) of the NMDA-induced release of NA using superfused hippocampal synaptosomes.The NMDA response was increased by SRIF-28 and SRIF-14, but not SRIF-28(1–14), whereas the release of [3H]-NA elicited by α-amino-3-hydroxy-5-methylisoxazide-4-propionic acid (AMPA) was unaffected. SRIF-14 did not mimic glycine at the NMDA receptor but activated SRIF receptors sited on noradrenergic terminals.The SRIF-14 effect was blocked by pertussis toxin but mimicked by mastoparan, a G-protein activator. BIM-23056, but not Cyanamid 154806, antagonized the SRIF-14 effect. This effect was mimicked by L362855, a partial agonist at the sst5 subtype, but not by the new selective sst1–sst4 receptor agonists L797591, L779976, L796778 and L803087.Protein kinase C (PKC) inhibitors (H7, staurosporine, GF 209103X, cheleritrine and sphingosine) prevented the SRIF-14 effect, while phorbol 12-myristate 13-acetate enhanced the NMDA response.SRIF-14 permitted NMDA receptor activation in the presence of 1.2 mM Mg2+ ions, both in hippocampal synaptosomes and slices. Blockade of inositol-1,4,5-trisphosphate (InsP3) receptors with heparin abolished the effect of SRIF-14.It is concluded that SRIF receptors, possibly of the sst5 subtype, can exert a permissive role on NMDA receptors colocalized on hippocampal noradrenergic terminals: activation of sst5 receptors is coupled to pertussis toxin-sensitive G proteins enhancing phosphoinositide metabolism with activation of InsP3 receptors and PKC; NMDA receptor subunits might be phosphorylated with consequent removal of the Mg2+ block in absence of depolarization.British Journal of Pharmacology (2000) 130, 557–566; doi:10.1038/sj.bjp.0703346
British Journal of Pharmacology 05/2000; 130(3):557 - 566. · 4.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Aniracetam, 1-(1,3-benzodioxol-5-yl-carbo-nyl)piperidine (1-BCP) and cyclothiazide, three compounds considered to enhance
cognition through modulation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors, were evaluated in the
‘kynurenate test’, a biochemical assay in which some nootropics have been shown to prevent the antagonism by kynurenic acid
of the N-methyl-d-aspartate (NMDA)-evoked [3H]noradrenaline ([3H]NA) release from rat hippocampal slices. Aniracetam attenuated the kynurenate (100 μM) antagonism of the [3H]NA release elicited by 100 μM NMDA with high potency (EC50≤0.1 μM). Cyclothiazide and 1-BCP were about 10 and 100 times less potent than aniracetam, respectively. The effect of aniracetam
persisted in the presence of the AMPA receptor antagonist 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione (NBQX) added at
5 μM, a concentration that did not affect NMDA receptors; in contrast, NBQX reduced the effect of 1-BCP and abolished that
of cyclothiazide. The AMPA-evoked release of [3H]NA from hippocampal slices or synaptosomes was enhanced by cyclothiazide, less potently by 1-BCP and weakly by aniracetam.
High concentrations of kynurenate (1 mM) antagonized the AMPA-evoked [3H]NA release in slices; this antagonism was attenuated by 1 μM cyclo-thiazide and reversed to an enhancement of AMPA-evoked
[3H]NA release by 10 μM of the drug, but was insensitive to 1-BCP or aniracetam. It is concluded that aniracetam exerts a dual
effect on glutamatergic transmission: modulation of NMDA receptor function at nanomolar concentrations, and modulation of
AMPA receptors at high micromolar concentrations. As to cyclothiazide and 1-BCP, our data concur with the idea that both compounds
largely act through AMPA receptors, although an NMDA component may be involved in the effect of 1-BCP.
Archiv für Experimentelle Pathologie und Pharmakologie 01/1999; 359(4):272-279. · 2.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The release of tritium from rat hippocampal synaptosomes prelabeled with [3H]noradrenaline ([3H]NA) or [3H]5-hydroxytryptamine ([3H]5-HT) and from rat neocortex synaptosomes prelabeled with [3H]choline and the release of endogenous GABA and glutamate from rat neocortex synaptosomes were monitored during superfusion
with media containing varying concentrations of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or kainic acid.
Concentration-dependent release potentiations were elicited by both excitatory amino acids (EAAs) in all the transmitter systems
investigated. The releases evoked by 100 µM AMPA were, in all cases, almost totally dependent on external Ca2+ and sensitive to 6,7-dinitroquinoxaline-2,3-dione (DNQX), indicating involvement of non-NMDA receptors. When cyclothiazide,
a drug able to prevent desensitization of AMPA-preferring receptors, was added to the superfusion medium (at 1 or 10 µM) concomitantly
with 100 µM AMPA or kainate, the EAA-evoked release of [3H]NA was significantly enhanced. Concanavalin A, a lectin thought to prevent desensitization of kainate-preferring receptors,
had no effect (up to 10 µM) on the release of [3H]NA evoked by AMPA or kainate. The effect of cyclothiazide was lost if, after an 8-min pretreatment, the drug was removed
just before the AMPA stimulus. When added concomitantly with the EAAs, cyclothiazide potentiated the release of [3H]5-HT elicited by AMPA and, less so, that evoked by kainate. Concanavalin A was ineffective. Neither cyclothiazide (1 or
10 µM) nor concanavalin A (3 or 10 µM) could affect the release of [3H]ACh or endogenous GABA provoked by 100 µM AMPA or kainate, suggesting that the receptors involved do not desensitize. Exposure
of neocortex synaptosomes to AMPA or kainate concomitantly with cyclothiazide caused endogenous glutamate release that did
not differ from that evoked by the EAAs alone. In contrast, the effects of AMPA and kainate were potentiated by concanavalin
A. The activity of the lectin (3 µM) persisted when it was applied for 8 min and then removed before the AMPA or kainate (100
µM) pulse. When hippocampal synaptosomes prelabeled with [3H]NA were subjected to three subsequent AMPA (100 µM) stimuli (S1, S2 and S3), the release of [3H]NA decreased dramatically from S1 to S3 (S3/S1 = 0.14 ± 0.04); a significant ‘protection’ of the AMPA effect was offered by 1 µM cyclothiazide (S3/S1 = 0.36 ± 0.06). This value did not differ from the S3/S1 ratio (0.38 ± 0.04) obtained in parallel experiments with 12 mM K+. The release evoked by high-K+ was insensitive to cyclothiazide. Finally, the effect of AMPA on the release of [3H]ACh did not respond to cyclothiazide also during three subsequent stimuli with 100 µM AMPA. To conclude: a) ionotropic non-NMDA
receptors mediating enhancement of NA, 5-HT, ACh, GABA and glutamate release exist on the corresponding nerve terminals; b)
the receptors present on noradrenergic and serotonergic neurons are AMPA-preferring receptors, whereas the glutamate autoreceptors
resemble most the kainate-preferring subtype; the receptors mediating ACh and GABA release can not be subclassified at present;
c) desensitization may not be a property of all non-NMDA ionotropic receptors. The receptors here characterized represent
five models of native non-NMDA receptors suitable for pharmacological and molecular studies.
Archiv für Experimentelle Pathologie und Pharmakologie 05/1997; 356(1):29-38. · 2.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Glutamate extracellular accumulation is an early event in brain ischemia triggering excitotoxic neuron damage. We have investigated how to control the glutamate efflux from human cerebrocortical slices superfused in conditions simulating an acute ischemic insult (oxygen and glucose deprivation). The efflux of previously accumulated [3H]D-aspartate or endogenous glutamate increased starting 18 min after exposure to ischemia and returned almost to basal values in 6 min reperfusion with standard medium. Superfusion with Ca2+-free, EGTA (0.5 mM)-containing medium or with medium containing tetrodotoxin (TTX; 0.5 μM) inhibited the ischemia (24 min)-evoked [3H]D-aspartate efflux by about 50% and 65%, respectively. The ischemia (24 or 36 min)-evoked efflux of [3H]D-aspartate or endogenous glutamate was reduced at least 40% by the adenosine A2A receptor antagonist SCH 58261 (1 μM); the compound was effective when added up to 15 min after exposure to ischemia. No effect of SCH 58261 on the ischemia-evoked [3H]D-aspartate was found in Ca2+-free, EGTA-containing medium. To conclude, a significant component of the ischemia-evoked glutamate efflux in human cerebrocortical slices seems to occur by a vesicular-like mechanism. Endogenously released adenosine is likely to activate A2A receptors that enhance vesicular-like glutamate release during ischemia; A2A receptor antagonists would deserve consideration for their neuroprotective potential.
Neuropharmacology.
