6-cyano-7-nitroquinoxaline-2-3-dione and 2-amino-3-phosphonopropionic-acid

The excitotoxicity cascade associated with energetic failure during and after cerebral ischemia involves the overactivation of glutamate receptors and intracellular calcium loading. We searched for synergistic neuroprotective effects of various drugs designed to prevent intracellular calcium influx in a model of oxygen-glucose deprivation (OGD) in cerebellar granule cells primary cultures. (5S,10R)-(-)-5-Methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801), D,L-2-Amino-3-phosphonopropionic acid (AP-3), 6-Cyano-7-nitroquinoxaline-2,3-dione disodium salt (CNQX) and Nifedipine were tested alone or in combinations. Treatments were applied during a two-hour OGD exposure and cellular outcome was assessed throughout 20-hour reoxygenation by the measurement of Propidium Iodide (PI) fluorescence. All treatments were able to prevent neuronal damage. OGD resulted in a mortality of 36.3±2.3% and 61.3±3.1% after 10 and 20 hours of reoxygenation, respectively. The most effective single treatment was AP-3 (3.3±1.4%; 17.9±2.6% mortality after 10 and 20 hours), followed in order by Nifedipine (7.2±1.6%; 20.1±3.0%), CNQX (8.5±2.5%; 20.0±3.5%), and MK-801 (14.9±2.6%; 39.3±6.4%). The combination of AP-3 with MK-801 showed a moderate synergistic effect (11.8±2.0% mortality at 20 hours), while the combinations of CNQX with Nifedipine and CNQX with MK-801, as well as the triple mix CNQX, Nifedipine and MK-801 failed to show a further improvement in the reduction of cellular death. In conclusion, targeting two mechanisms of cellular demise (ionotropic receptors and metabotropic glutamate receptors) provided an advantage against several unimodal strategies (blocking calcium entry through ionotropic glutamate receptors and L-type calcium channels). Our results suggest that a multimodal combinatorial treatment strategy in cerebral ischemia may increase neuroprotective efficacy and call for further research.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Cell Death; Cells, Cultured; Cerebellum; Dizocilpine Maleate; Drug Therapy, Combination; Fluorescence; Glucose; Nifedipine; Oxygen; Propidium; Rats

The present study investigated the involvement of spinal glutamate receptors in the induction and maintenance of the pain-related behaviors induced by the venom of scorpion Buthus martensi Karsch (BmK). (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5-10-imine hydrogen maleate (MK-801; 40nmol; a non-competitive NMDA receptor antagonist), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 40nmol; a non-NMDA receptor antagonist), dl-amino-3-phosphonopropionic acid (dl-AP3; 100nmol; a group I metabotropic glutamate receptor antagonist) and 4-aminopyrrolidine-2,4-dicarboxylate (APDC; 100nmol; a group II metabotropic glutamate receptor agonist) were employed. On intrathecal injection of glutamate receptor antagonists/agonist before BmK venom administration by 10min, BmK venom-induced spontaneous nociceptive responses could be suppressed by all tested agents. Primary thermal hyperalgesia could be inhibited by MK-801 and dl-AP3, while bilateral mechanical hyperalgesia could be inhibited by CNQX and dl-AP3 and contralateral mechanical hyperalgesia could be inhibited by APDC. On intrathecal injection of glutamate receptor antagonists/agonist after BmK venom injection by 4.5h, primary thermal hyperalgesia could be partially reversed by all tested agents, while bilateral mechanical hyperalgesia could only be inhibited by APDC. The results suggest that the role of spinal glutamate receptors may be different on the various manifestations of BmK venom-induced pain-related behaviors.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Injections, Spinal; Male; Pain; Proline; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Scorpion Venoms

The involvement of type I metabotropic glutamate receptors in hippocampal CA1 long-term potentiation (LTP) depends on the applied tetanic stimulation protocol. Activation of these receptors may cause an elevation of intracellular calcium via the formation of the second messenger inositol triphosphate (IP3) and subsequent intracellular calcium release. It has been shown that the type I metabotropic receptors antagonist L-2-amino-3-phosphonopropionate (L-AP3) blocks CA1 LTP. Combining dendritic calcium and field potential measurements in CA1 hippocampal area, we found that L-AP3 did not affect single calcium transients but reduced the calcium changes evoked by a single tetanus, preventing the long-lasting calcium enhancements associated with CA1 LTP. These findings suggest that the formation of this type of LTP requires calcium release from IP3-sensitive stores.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Calcium; Calcium Signaling; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Fluorescent Dyes; Fura-2; Hippocampus; Inositol 1,4,5-Trisphosphate; Intracellular Fluid; Long-Term Potentiation; Neurons; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission; Up-Regulation

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Cell Survival; Cells, Cultured; Chick Embryo; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Methylmalonic Acid; Neurons; Neuroprotective Agents; Neurotoxins; NG-Nitroarginine Methyl Ester; Piperidines

The receptor mechanisms by which the selective cannabinoid CB1 receptor antagonist/inverse agonist, SR 141716A [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyraz ole-carboxamide] produces scratching and head-twitch response (HTR) in naive mice were examined. Acute intraperitoneal administration of varying doses of SR 141716A produced both scratchings (ED50 = 3.9 mg/kg) and head-twitches (ED50 = 4.6 mg/kg) in a dose-dependent manner. A dose of 10 mg/kg SR 141716A was used to induce the cited behaviors for drug interaction studies. The selective 5-HT2A/C receptor antagonist, SR 46349B [trans-4-[(3Z)3-(2-dimethylaminoethyl) oxyimino-3-(2-fluorophenyl) propen-1-yl] phenol] potently and completely blocked the head-twitches produced by SR 141716A (ID50 = 0.08 mg/kg). The induced scratching behavior was partially (68%) and less potently (ID50 = 0.6 mg/kg) blocked by SR 46349B pretreatment. The AMPA/kainate receptor antagonist, CNQX [6-cyano-7-nitroquinoxaline-2,3-dione], partially attenuated (68-78%) the induced scratching and head-twitching behaviors. On the contrary, the selective NMDA antagonist, AP-3 [(+/-)-2-amino-3-phosphonopropionic acid], had no significant effect on these behaviors. The selective tachykinin NK1 antagonist, CP 94, 994 [(+/-)-(2S, 3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine], also partially attenuated both the scratching (64%) and the head-twitching (76%) symptoms produced by SR 141716A. Since SR 141716A lacks affinity for the discussed receptors, it appears that the induction of the cited behaviors probably involve indirect activation of their respective neurotransmitter systems.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Behavior, Animal; Dose-Response Relationship, Drug; Dronabinol; Excitatory Amino Acid Antagonists; Fluorobenzenes; Glutamic Acid; Head Movements; Injections, Intraperitoneal; Male; Mice; Mice, Inbred ICR; Neurotransmitter Agents; Phenols; Piperidines; Psychotropic Drugs; Pyrazoles; Receptors, Cannabinoid; Receptors, Drug; Rimonabant; Serotonin; Serotonin Antagonists; Tachykinins

Intravenous administration of N-methyl-D-aspartate (NMDA) receptor antagonists and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonists reportedly reduce the minimum alveolar anaesthetic concentration (MAC) for inhalation anaesthetics. If pain perception can be prevented by the intrathecal administration of antinociceptive receptor antagonists, these agents may reduce the requirements for inhalation anaesthetics. We studied the effect of intrathecal administration of an AMPA/kainate receptor antagonist, a metabotropic glutamate (mGlu) receptor antagonist and co-administration of NMDA and a neurokinin-1(NK-1) receptor antagonist drugs at low doses on the MAC.. After Wistar rats (n=36) were fitted with indwelling intrathecal catheters, the MAC of isoflurane was determined following intrathecal administration of a non-NMDA receptor antagonist (CNQX) at 10 microg, a mGlu receptor antagonist (AP3) at 10 microg, or a combination of NMDA receptor antagonist (APV) at 0.01 microg to 1 microg with NK-1 receptor antagonist (CP96345, CP) at 0.1 microg to 10 microg. Subsequently, a reversal dose of intrathecal NMDA with substance P (SP) was administered, and the MAC of isoflurane was redetermined. Conscious rats (n=15) were also examined for the presence of locomotor dysfunction following the intrathecal co-administration of APV and CP.. Neither CNQX nor AP3 reduced the MAC of isoflurane. APV at 0.01 microg plus CP at 1 microg, as well as APV at 0.1 microg plus CP at 10 microg, reduced the MAC of isoflurane, with respective reductions of 7.6% and 14%; (P<0.05). Co-administration of NMDA plus SP reversed the decrease in the MAC of isoflurane. Locomotive activity was not changed.. The NMDA receptor and the NK-1 receptor are important determinants of the MAC of isoflurane, exerting this influence by inhibition of pain transmission in the spinal cord, while mGlu and AMPA receptors have no effect on the MAC of isoflurane.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Anesthetics, Inhalation; Animals; Biphenyl Compounds; Catheters, Indwelling; Drug Combinations; Excitatory Amino Acid Antagonists; Injections, Spinal; Isoflurane; Locomotion; Male; Neurokinin-1 Receptor Antagonists; Nociceptors; Pain; Rats; Rats, Wistar; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Substance P; Synaptic Transmission; Valine

In view of the neurotrophic effect of vasoactive intestinal peptide (VIP), the regulation of brain-derived neurotrophic factor (BDNF) expression by VIP and the related peptide pituitary adenylate cyclase-activating polypeptide (PACAP) was analysed by Northern blot in primary cultures of cortical neurones. Results reported in this article demonstrate that VIP and PACAP stimulate the expression of BDNF mRNA in primary cultures of cortical neurones and astrocytes. In primary cultures of cortical neurones, induction of BDNF mRNA by VIP and PACAP is completely inhibited by the N-methyl-D-aspartate (NMDA) receptor antagonists MK-801 and AP5, therefore indicating that VIP and PACAP do not stimulate BDNF expression directly but rather by potentiating the effect of glutamate tonically released by neurones and acting at NMDA receptors. In addition to its neurotrophic effects, BDNF has been shown to be involved in neuronal plasticity and results reported here suggest that by stimulating BDNF expression, VIP and PACAP could modulate synaptic plasticity in the cerebral cortex.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Astrocytes; Blotting, Northern; Brain-Derived Neurotrophic Factor; Cells, Cultured; Cerebral Cortex; Dizocilpine Maleate; Drug Synergism; Excitatory Amino Acid Antagonists; Gene Expression; Glutamic Acid; Mice; Neuronal Plasticity; Neurons; Neuropeptides; Neurotransmitter Agents; Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, N-Methyl-D-Aspartate; RNA, Messenger; Vasoactive Intestinal Peptide

Intracellular recordings were obtained from neocortical brain slices of adult rats maintained in vitro. The effect of metabotropic glutamate receptor activation on spike frequency adaptation in regular spiking layer II and III neurons was determined. Putative metabotropic glutamate receptor agonists and antagonists, as well as inhibitors of intracellular signaling systems, were tested. Activation of metabotropic glutamate receptors by bath applied (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD; 50-200 microM) reduced the first interspike interval and increased action potential frequency at all current intensities. This effect was not blocked by ionotropic glutamate receptor antagonists. Under these recording conditions, quisqualate (1-10 microM) similarly reduced spike frequency adaptation. Neither 1R,3S-ACPD, L-2-carboxycyclopropylglycine-I nor the putative presynaptic metabotropic glutamate receptor agonist, L-2-amino-4-phosphonobutyrate, mimicked the effects of 1S,3R-ACPD or quisqualate. Bath application of the putative metabotropic glutamate receptor antagonist, alpha-methyl-4-carboxyphenylglycine, competitively antagonized the excitatory actions of 1S,3R-ACPD. Another putative antagonist, L-2-amino-3-phosphonopropionate, failed to antagonize the reduction in spike frequency adaptation. Intracellular injection of guanosine-5'-O-(2-thiodiphosphate), a non-hydrolysable analog of GTP, inhibited the postsynaptic metabotropic glutamate receptor-mediated effects. However, the depression of synaptic transmission by 1S,3R-ACPD was not antagonized by this compound. The decrease in spike frequency adaptation by 1S,3R-ACPD was not prevented by prior exposure to the non-specific protein kinase inhibitors H-7 or H-8 (10 microM), the protein kinase A inhibitor H-89 (0.25 microM) or the protein kinase C inhibitor staurosporine (0.10 microM). These data suggest that the metabotropic glutamate receptor-mediated reduction in spike adaptation requires the activation of specific G-protein-coupled metabotropic glutamate receptor subtypes located on postsynaptic sites. The increase in neuronal excitability observed in the adult neocortex may be mediated either by an unidentified G-protein-coupled second messenger or via a membrane-delimited G-protein action.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Adult; Alanine; Amino Acids, Dicarboxylic; Animals; Benzoates; Cycloleucine; Enzyme Inhibitors; Frontal Lobe; Glycine; GTP-Binding Proteins; Guanosine Diphosphate; Humans; Isoquinolines; N-Methylaspartate; Nerve Tissue Proteins; Neurons; Protein Kinase Inhibitors; Protein Kinases; Quisqualic Acid; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Signal Transduction; Staurosporine; Sulfonamides; Thionucleotides

Exposure of cultured cerebellar neurons to the putative metabotropic glutamate receptor antagonist L-2-amino-3-phosphonopropionate (L-AP3) for 24 h produced a neurotoxic effect which was prevented by the addition of the NMDA receptor antagonist (+)-10,11-dihydro-5-methyl-5-H-dibenzo-[a,d]-cyclohepten-5,1 0-imine hydrogen maleate (MK-801). MK-801 did also reduce neurotoxicity following 72 h exposure to L-AP3 neurotoxicity in the presence of MK-801 was antagonized by glutamate. Our results suggest that metabotropic glutamate receptors may play an important role in neuronal survival by controlling NMDA receptor-dependent as well as independent pathways.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Cell Survival; Cells, Cultured; Cerebellum; Dizocilpine Maleate; Neurons; Rats; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate

We investigated the activation of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) via stimulation of glutamate receptors and subsequent phosphorylation of vimentin and glial fibrillary acidic protein (GFAP) in cultured rat cortical astrocytes. The indirect immunofluorescence analysis with the anti-CaM kinase II antibody revealed that the enzyme was detected diffusely in the cytoplasm and more intensely in the nucleus. Glutamate elevated the Ca(2+)-independent activity of CaM kinase II through autophosphorylation, and this response was blocked by both DL-2-amino-3-phosphonopropionate and 6-cyano-7-nitroquinoxaline-2,3-dione, but not by D-2-amino-5-phosphonovalerate. In the experiments using 32P-labeled astrocytes, the phosphorylation of vimentin and GFAP as well as autophosphorylation of CaM kinase II were found to be stimulated after the exposure to glutamate. It was concluded by two-dimensional phosphopeptide analysis that the increased phosphorylation of vimentin and GFAP observed in intact cells were due to the activation of CaM kinase II by glutamate. These results suggest that glutamate can activate CaM kinase II through stimulation of both the metabotropic and non-N-methyl-D-aspartate receptors, and that the concomitant phosphorylation of vimentin and GFAP may in turn regulate the functions of intermediate filament proteins in intact astrocytes.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Animals, Newborn; Astrocytes; Calcium-Calmodulin-Dependent Protein Kinases; Cells, Cultured; Cerebral Cortex; Dizocilpine Maleate; Electrophoresis, Polyacrylamide Gel; Fluorescent Antibody Technique; Glial Fibrillary Acidic Protein; Glutamates; Glutamic Acid; Immunoblotting; Ionomycin; Molecular Weight; Phosphoproteins; Phosphorylation; Quinoxalines; Rats; Rats, Wistar; Receptors, Glutamate; Tetradecanoylphorbol Acetate; Vimentin

1. Intracellular recordings from postnatal 2- to 12-day-old (P2-12) rat hippocampal CA3 pyramidal neurones exhibited spontaneous synaptic potentials mediated by GABAA receptors. These potentials can be separated on the basis of amplitude into two classes which are referred to as small and large. 2. The large depolarizing potentials were reversibly inhibited by the Zn2+ chelator 1,2-diethyl-3-hydroxypyridin-4-one (CP94). The small inhibitory postsynaptic potentials. (IPSPs) were apparently unaffected. 3. Stimulation of the mossy fibre pathway evoked composite excitatory postsynaptic potentials (EPSPs) and IPSPs. Threshold stimulus-evoked synaptic potentials were mediated by GABAA receptors and were reversibly blocked by CP94. The responses evoked by suprathreshold stimulation and persisting in the presence of bicuculline or CP94 were partially inhibited by 2-amino-5-phosphonopropionic acid (AP5) and were completely blocked with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 4. L-Histidine, which preferentially forms complexes with Cu2+ > Zn2+ > Fe2+ > Mn2+, inhibited both naturally occurring spontaneous and evoked GABAA-mediated large synaptic potentials without affecting the neuronal resting membrane properties. Exogenously applied Zn2+ induced large spontaneous synaptic potentials and prolonged the duration of the evoked potentials. These effects were reversibly blocked by histidine. 5. The metal chelating agent diethyldithiocarbamate had little effect on the large amplitude synaptic potentials. 6. The transition metal divalent cations Fe2+ and Mn2+ did not initiate large synaptic potentials in CA3 neurones; however, Cu2+ depolarized the membrane and enhanced both excitatory and inhibitory synaptic transmission, resulting in a transient increase in the frequency of the large amplitude events. In comparison, zinc increased the frequency of the large potentials and also induced such events in neurons (P4-21) where innate potentials were absent. The postsynaptic response to ionophoretically applied GABA was either unaffected or slightly enhanced by Zn2+. 7. Under conditions favouring the activation of non-NMDA receptors, excitatory synaptic transmission was unaffected by CP94 but was depressed by Zn2+. Responses to ionophoretically applied glutamate were not inhibited by Zn2+, indicating that Zn2+ affects excitatory synaptic transmission via a presynaptic mechanism. 8. We conclude that the naturally occurring large synaptic potentials in young CA3 neurones ar

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Aging; Alanine; Animals; Animals, Newborn; Bicuculline; Cations, Divalent; Chelating Agents; Electric Stimulation; Evoked Potentials; gamma-Aminobutyric Acid; Hippocampus; Histidine; In Vitro Techniques; Iron Chelating Agents; Pyramidal Tracts; Pyridones; Rats; Rats, Wistar; Receptors, GABA-A; Synaptic Transmission; Zinc

The effects of dithiothreitol (DTT) and, reduced (GSH) and oxidized (GSSG), glutathione on the release of [3H]GABA evoked by glutamate and its agonists were studied in rat hippocampal slices. DTT had no effect on the basal release of [3H]GABA but it enhanced and prolonged the glutamate agonist-evoked release. This effect was abolished by (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohept-5,10-imine hydrogen maleate (MK-801), a noncompetitive NMDA antagonist, and blocked by Mg2+ ions. It was only slightly attenuated by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, and not affected by L-(+)-2-amino-3-phosphonopropionate (L-AP3), a selective antagonist of the metabotropic glutamate receptor. The effect of DTT on the NMDA-evoked release of GABA was only slightly affected by extracellular Ca2+ but completely blocked by verapamil even in the absence of Ca2+. GSH and GSSG attenuated or abolished the effects of DTT on the agonist-induced release of [3H]GABA. The results imply that the enhanced and prolonged release of GABA evoked by the coexistence of DTT and excitatory amino acids and attenuated by endogenous GSH and GSSG is a consequence of sustained activation of the NMDA receptor-governed ionophores, which contain functional thiol groups. DTT, GSH and GSSG may regulate the redox state and accessibility of these groups. In addition to the influx of extracellular Ca2+, DTT mobilizes Ca2+ from intracellular pools distinct from those regulated by metabotropic glutamate receptors.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Dithiothreitol; Dizocilpine Maleate; GABA Agonists; gamma-Aminobutyric Acid; Glutathione; Glycine; Hippocampus; In Vitro Techniques; Kinetics; Magnesium; Male; N-Methylaspartate; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Tritium

To investigate the electrophysiological effects of the stimulation of the metabotropic excitatory amino acid receptors, we applied trans-1-amino-cyclopentane-1,3-dicarboxylate, an agonist of this type of receptors, on presumed rat dopamine cells intracellularly recorded in vitro. Trans-1-amino-cyclopentane-1,3-dicarboxylate (3-30 microM, t-ACPD) caused a sustained increase of the spontaneous firing rate and a depolarization. When the membrane potential was held at about the resting level (-50, -60 mV), by the single-electrode voltage-clamp technique, t-ACPD induced an inward current. In 57% of the tested cells the inward current was associated with a decrease of the apparent input conductance. In the remaining cells no obvious changes in membrane conductance were observed. The active form of t-ACPD, (1S,3R)-1-amino-cyclopentane-1,3-dicarboxylate [3-50 microM, (1S,3R)-ACPD] also produced a reversible inward current on the dopaminergic cells and this was antagonized by (S)-4-carboxy-3-hydroxyphenylglycine (300 microM), a selective antagonist of the (1S,3R)-ACPD-induced depolarization on central neurons. The (1S,3R)-ACPD-induced inward current was not antagonized by L-2-amino-3-phosphonopropionic acid (100 microM), an antagonist of the t-ACPD-induced activation of inositide synthesis. 6-cyano-7-nitroquinoxaline-2,3-dione (10 microM), an alfa-amino-3-hydroxy-5- methyl-isoxazole propionic acid/kainate antagonist, DL-amino-5-phosphonopentanoic acid (30 microM), an N-methyl-D-aspartate antagonist, and scopolamine (10 microM), a muscarinic antagonist, did not significantly affect the actions of t-ACPD. A block of synaptic transmission obtained by applying tetrodotoxin failed to prevent the action of t-ACPD.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Alanine; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Cycloleucine; Dopamine; Electrophysiology; Female; Glycine; Male; Neurons; Potassium; Quinoxalines; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Stimulation, Chemical; Tetrodotoxin

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Aspartic Acid; Cells, Cultured; Cerebellum; Excitatory Amino Acid Antagonists; Ibotenic Acid; Kinetics; Membrane Potentials; Purkinje Cells; Receptors, Metabotropic Glutamate; Time Factors; Virulence Factors, Bordetella

The neuroprotective characteristics of the functional antagonist of metabotropic stimulated phosphoinositide hydrolysis, 2-amino-3-phosphonoproprionate (D,L-AP3), were examined alone and in combination with the non-competitive N-methyl-D-aspartate (NMDA) antagonist, MK-801, against ibotenate induced brain injury. Postnatal day (PND) 7 rats received unilateral stereotaxic intrastriatal injections of 10 nmol ibotenate and treated with either D,L-AP3 (600 nmol i.c.), MK-801 (1 mg/kg i.p.) or both. The severity of brain injury was assessed on PND 12 by comparison of the weights of injected and contralateral cerebral hemispheres. Ibotenate induced injury was partially reduced by treatment with MK-801 (34.0 +/- 4.4% protection, P < 0.05 vs. PBS treated, independent t-test) but not D,L-AP3. However, combined treatment with both MK-801 and D,L-AP3 produced marked synergistic neuroprotection (83.5 +/- 7.6% protection, P < 0.001 vs. PBS treated, independent t-test). The data suggest that metabotropic stimulated phosphoinositide hydrolysis contributes to excitotoxic neuronal injury in the presence of concurrent ionotropic receptor activation.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Brain; Brain Diseases; Dizocilpine Maleate; Drug Synergism; Female; Ibotenic Acid; Injections; Male; Organ Size; Quinoxalines; Rats; Rats, Sprague-Dawley

An amino acid, 3,5-dihydroxyphenylglycine (DHPG) induced current responses in Xenopus oocytes expressing a metabotropic glutamate receptor clone mGluR1. Apparent EC50 of DHPG for mGluR1 was slightly lower than that of (+-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD). DHPG responses were partially inhibited by 2-amino-3-phosphonopropionic acid (AP-3). DHPG had no effect on ionotropic glutamate receptors whose expression was induced in the oocytes following injection of poly(A)+ mRNA of rat brains. In hippocampal slices, DHPG produced slow excitation of pyramidal cells, resulting from a depression of Ca(2+)-dependent K+ current and a voltage-dependent K+ current. These results indicate that DHPG is a specific and potent agonist of mGluRs.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Cycloleucine; Egtazic Acid; Glycine; Hippocampus; In Vitro Techniques; Male; Oocytes; Potassium Channels; Quinoxalines; Rats; Rats, Wistar; Receptors, Glutamate; Resorcinols; RNA, Messenger; Xenopus

A detailed pharmacological characterization of the quisqualate (QA) receptor coupled to phospholipase C (Qp) was performed in striatal neurons. The experiments were carried out in the presence of the ionotropic antagonists MK-801 (1 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (30 microM), concentrations that block N-methyl-D-aspartate (NMDA) or alpha-amino-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in these cells. QA, ibotenate and trans-1-aminocyclopentyl-1,3-dicarboxylate (ACPD) evoked dose-dependent inositol phosphate formations with EC50 values of 0.3, 6.7 and 29 microM, respectively. QA and ibotenate had the same maximal effect (295.7 +/- 17.9% of basal, n = 6) whereas the efficacy of ACPD was somewhat lower (70.2 +/- 8.9% of the maximal quisqualate effect, n = 4). The QA-, ibotenate- and ACPD-induced maximal effects were not additive, and the inositol phosphate formations induced by high concentrations of L-aspartate (L-ASP), AMPA, kainate (KA) and domoate (DO) (100 microM or higher) were also not additive. The inositol phosphate responses induced by all these agonists were totally blocked by the phorbol ester phorbol 12,13-dibutyrate (PdBu), but not by atropine or prazosin suggesting that all these substances were able to stimulate the Qp excitatory amino acid receptor in striatal neurons. Of the excitatory amino acid receptor antagonists tested, only D,L-2-amino-3-phosphonopropionate (D,L-AP3) inhibited QA-induced InsP formation in a competitive manner (mean pKi = 4.45 +/- 0.43, n = 4). However, this drug was also a partial agonist of the Qp receptor 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). The Qp excitatory amino acid receptor in striatal neurons therefore closely resembles Qp receptors with high potency for agonists as described in striatal and retinal slices and synaptoneurosomes, and has several pharmacological differences compared to the Qp receptors which have low potency for agonists described in hippocampal and cortical slices, cerebellar granule cells, astrocytes and rat brain mRNA-injected oocytes.

Topics: 2-Aminoadipic Acid; 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Aminobutyrates; Animals; Cells, Cultured; Corpus Striatum; Dizocilpine Maleate; Fura-2; Ibotenic Acid; Inositol Phosphates; Kainic Acid; Mice; Neurons; Phorbol 12,13-Dibutyrate; Phosphoserine; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Type C Phospholipases

We have investigated the roles of glutamate (Glu) receptors in the mechanism of long-term potentiation observed in rat hippocampal mossy fiber synapses (MF-LTP). The mossy fiber responses were almost completely suppressed by ionotropic Glu receptor (iGluR) antagonists both before and after the induction of LTP. However, tetanic stimulation produced robust LTP even when the synaptic transmission was blocked postsynaptically by iGluR antagonists. In contrast, when the transmission was blocked presynaptically by Ca(2+)-free media, tetanic stimulation produced no LTP. D,L-2-amino-3-phosphono-propionate(D,L-AP3), a metabotropic Glu receptor (mGluR) antagonist, inhibited the induction of MF-LTP. Perfusion with ibotenate, a mGluR agonist, induced long-lasting enhancement of the mossy fiber responses without tetanic stimulation, and this ibotenate-induced potentiation was antagonized by D,L-AP3.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Alanine; Animals; Evoked Potentials; Hippocampus; Ibotenic Acid; In Vitro Techniques; Male; Perfusion; Pyramidal Tracts; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, Glutamate; Receptors, Neurotransmitter; Synapses; Synaptic Transmission