6-cyano-7-nitroquinoxaline-2-3-dione and 2-(2-3-dicarboxycyclopropyl)glycine

The hippocampal CA3 area contains large amounts of vesicular zinc in the mossy fiber terminals which is released during synaptic activity, depending on presynaptic calcium. Another characteristic of these synapses is the presynaptic localization of high concentrations of group II metabotropic glutamate receptors, specifically activated by DCG-IV. Previous work has shown that DCG-IV affects only mossy fiber-evoked responses but not the signals from associational-commissural afferents, blocking mossy fiber synaptic transmission. Since zinc is released from mossy fibers even for single stimuli and it is generally assumed to be co-released with glutamate, the aim of the work was to investigate the effect of DCG-IV on mossy fiber zinc signals.. Studies were performed using the membrane-permeant fluorescent zinc probe TSQ, and indicate that DCG-IV almost completely abolishes mossy fiber zinc changes as it does with synaptic transmission.. Zinc signaling is regulated by the activation of type II metabotropic receptors, as it has been previously shown for glutamate, further supporting the corelease of glutamate and zinc from mossy fibers.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Anticonvulsants; Cyclopropanes; Excitatory Amino Acid Antagonists; Glutamic Acid; Glycine; Hippocampus; Mossy Fibers, Hippocampal; Presynaptic Terminals; Rats, Wistar; Receptors, Metabotropic Glutamate; Signal Transduction; Statistics, Nonparametric; Synaptic Transmission; Synaptic Vesicles; Zinc

Metabotropic glutamate (mGlu) receptors modulate pain from within the midbrain periaqueductal grey (PAG). In the present study, the postsynaptic mGlu receptor mediated effects on rat PAG neurons were examined using whole-cell patch-clamp recordings in brain slices. The selective group I agonist DHPG (10 μM) produced an inward current in all PAG neurons tested which was associated with a near parallel shift in the current-voltage relationship. By contrast, the group II and III mGlu receptor agonists DCG-IV (1 μM) and l-AP4 (3 μM) produced an outward current in only 10-20% of PAG neurons tested. The DHPG induced current was concentration dependent (EC(50) = 1.4 μM), was reduced by the mGlu1 antagonist CPCCOEt (100 μM), and was further reduced by CPCCOEt in combination with the mGlu5 antagonist MPEP (10 μM). The glutamate transport blocker TBOA (30 μM) also produced an inward current, however, this was largely abolished by CNQX (10 μM) plus AP5 (25 μM). Slow EPSCs were evoked following train, but not single shock stimulation, which were enhanced by TBOA (30 μM). The TBOA enhancement of slow EPSCs was abolished by MPEP plus CPCCOEt. These findings indicate that endogenously released glutamate, under conditions in which neurotransmitter spill-over is enhanced, activates group I mGlu receptors to produce excitatory currents within PAG. Thus, postsynaptic group I mGlu receptors have the potential to directly modulate the analgesic, behavioural and autonomic functions of the PAG. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Aminobutyrates; Animals; Aspartic Acid; Chromones; Cyclopropanes; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Female; Glycine; Male; Membrane Potentials; Methoxyhydroxyphenylglycol; Neurons; Periaqueductal Gray; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate

Profound activity-dependent synaptic facilitation at hippocampal mossy fiber synapses is a unique and functionally important property. Although presynaptic ionotropic receptors, such as kainate receptors, contribute partially to the facilitation in the hippocampus, the precise mechanisms of presynaptic regulation by endogenous neurotransmitters remain unclear. In this study, we report that axonal GABA(A) receptors on mossy fibers are involved in the activity-dependent facilitation during development. In immature mouse hippocampal slices, short-train stimulation (five pulses at 25 Hz) caused frequency-dependent facilitation of not only postsynaptic responses but also presynaptic fiber volleys that represent presynaptic activities. This fiber volley facilitation was inhibited by selective GABA(A) receptor antagonists, or by enkephalin that selectively suppresses excitability of interneurons. Furthermore, we directly demonstrated that this facilitation resulted from depolarization of mossy fibers in imaging experiments using a voltage-sensitive dye. This increased mossy fiber excitability caused by depolarizing action of GABA gradually decreased with development and eventually disappeared at around postnatal day 30. These results suggested that GABA released from interneurons acted on axonal GABA(A) receptors on mossy fibers and contributed at least partially to the activity- and age-dependent facilitation in the hippocampus.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Axons; Bicuculline; Cyclopropanes; Enkephalin, Methionine; Excitatory Postsynaptic Potentials; Fluorescent Dyes; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid; Glycine; Hippocampus; Interneurons; Male; Mice; Mice, Inbred C57BL; Mossy Fibers, Hippocampal; Muscimol; Patch-Clamp Techniques; Picrotoxin; Presynaptic Terminals; Pyridazines; Pyridinium Compounds; Receptors, GABA-A; Synaptic Transmission; Tetrodotoxin

Hippocampal mossy fiber synapses show unique molecular features and dynamic range of plasticity. A recent paper proposed that the defining features of mossy fiber synaptic plasticity are caused by a local buildup of extracellular adenosine (Moore et al., 2003). In this study, we reassessed the role of ambient adenosine in regulating mossy fiber synaptic plasticity in mouse and rat hippocampal slices. Synaptic transmission was highly sensitive to activation of presynaptic adenosine A1 receptors (A1Rs), which reduced transmitter release by >75%. However, most of A1Rs were not activated by ambient adenosine. Field potentials increased only by 20-30% when A1Rs were fully blocked with the A1R antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (1 microM). Moreover, blocking A1Rs hardly altered paired-pulse facilitation, frequency facilitation, or posttetanic potentiation. Frequency facilitation was similar in A1R-/- mice and when measured with NMDA receptor-mediated EPSCs in CA3 pyramidal cells in the presence of DPCPX. Additional experiments suggested that the results obtained by Moore et al. (2003) can partially be explained by their usage of a submerged recording chamber and elevated divalent cation concentrations. In conclusion, a reduction of the basal release probability by ambient adenosine does not underlie presynaptic forms of plasticity at mossy fiber synapses.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Adenine; Adenosine; Adenosine A1 Receptor Antagonists; Animals; Animals, Newborn; Bicuculline; Cyclopentanes; Cyclopropanes; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; Glycine; In Vitro Techniques; Mice; Mice, Inbred C57BL; Mice, Knockout; Mossy Fibers, Hippocampal; Neuronal Plasticity; Neurons; Patch-Clamp Techniques; Rats; Rats, Wistar; Receptor, Adenosine A1; Synapses; Synaptic Transmission; Xanthines

While group II metabotropic glutamate receptors (mGluRs) are known to be expressed in the rat globus pallidus (GP), their functions remain poorly understood. We used standard patch clamping technique in GP slices to determine the effect of group II mGluR activation on excitatory transmission in this region. Activation of group II mGluRs with the group-selective agonist DCG-IV or APDC reduced the amplitude of the evoked excitatory postsynaptic currents (EPSCs) and significantly increased the paired pulse ratio suggesting a presynaptic site of action. This was further supported by double-labeling electron microscopy data showing that group II mGluRs (mGluR2 and 3) immunoreactivity is localized in glutamatergic pre-terminal axons and terminals in the GP. Furthermore, we found that LY 487379, an mGluR2-specific allosteric modulator, significantly potentiated the inhibitory effect of DCG-IV on the excitatory transmission in the GP. Co-incubation with 30 microM LY 487379 increased the potency of DCG-IV about 10-fold in the GP. We were thus able to pharmacologically isolate the mGluR2-mediated function in the rat GP using an mGluR2-specific allosteric modulator. Therefore, our findings do not only shed light on the functions of group II mGluRs in the GP, they also illustrate the therapeutic potential of mGluR-targeting allosteric modulators in neurological disorders such as Parkinson's disease.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Aminobutyrates; Anesthetics, Local; Animals; Animals, Newborn; Cyclopropanes; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Globus Pallidus; Glycine; In Vitro Techniques; Lidocaine; Membrane Potentials; Methoxyhydroxyphenylglycol; Neurons; Patch-Clamp Techniques; Proline; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Sulfonamides; Synaptic Transmission; Xanthenes

The hippocampal mossy fiber terminals of CA3 area contain high levels of vesicular zinc that is released in a calcium-dependent way, following high-frequency stimulation. However the properties of zinc release during normal synaptic transmission, paired-pulse facilitation and mossy fiber long-term potentiation are still unknown. Using the fluorescent zinc probe N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide, we measured fast mossy fiber zinc changes indicating that zinc is released following single and low levels of electrical stimulation. The observed presynaptic zinc signals are maintained during the expression of mossy fiber long-term potentiation, assumed to be mediated by an increase in transmitter release, and are enhanced during paired-pulse facilitation. This zinc enhancement is, like paired-pulse facilitation, reduced during established long-term potentiation. The correlation between the paired-pulse evoked zinc and field potential responses supports the idea that zinc is co-released with glutamate.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Aminoquinolines; Animals; Anticonvulsants; Cholinesterase Inhibitors; Cyclopropanes; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Ethylenediamines; Excitatory Amino Acid Antagonists; Fluorescent Dyes; GABA Antagonists; Glycine; In Vitro Techniques; Long-Term Potentiation; Mossy Fibers, Hippocampal; Picrotoxin; Rats; Rats, Inbred WF; Synapses; Time Factors; Tosyl Compounds; Zinc

It has been suggested recently that presynaptic kainate receptors (KARs) are involved in short-term and long-term synaptic plasticity at hippocampal mossy fiber synapses. Using genetic deletion and pharmacology, we here assess the role of GLU(K5) and GLU(K6) in synaptic plasticity at hippocampal mossy fiber synapses. We found that the kainate-induced facilitation was completely abolished in the GLU(K6)-/- mice, whereas it was unaffected in the GLU(K5)-/-. Consistent with this finding, synaptic facilitation was reduced in the GLU(K6)(-/-) and was normal in the GLU(K5)-/-. In agreement with these results and ruling out any compensatory effects in the genetic deletion models, application of the GLU(K5)-specific antagonist LY382884 [(3S,4aR,6S,8aR)-6-(4-carboxyphenyl)methyl-1,2,3,4,4a,5,6,7,8,8a-decahydroisoquinoline-3-carboxylic acid] did not affect short-term and long-term synaptic plasticity at the hippocampal mossy fiber synapses. We therefore conclude that the facilitatory effects of kainate on mossy fiber synaptic transmission are mediated by GLU(K6)-containing KARs.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids, Dicarboxylic; Animals; Benzodiazepines; Cyclopropanes; Excitatory Postsynaptic Potentials; Gene Deletion; GluK2 Kainate Receptor; Glycine; Isoquinolines; Isoxazoles; Kainic Acid; Mice; Mice, Knockout; Mossy Fibers, Hippocampal; Neuronal Plasticity; Patch-Clamp Techniques; Potassium; Propionates; Rats; Rats, Sprague-Dawley; Rats, Wistar; Receptors, Kainic Acid; Synaptic Transmission

Patch pipettes were used to record currents in whole-cell configuration to study the effects of group II metabotropic glutamate receptor (mGluR) stimulation on synaptic transmission in slices of rat subthalamic nucleus. Evoked glutamatergic excitatory postsynaptic currents (EPSCs) were reversibly reduced by the selective group II mGluR agonist (2'S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG IV) in a concentration-dependent manner, with an IC50 of 0.19 +/- 0.05 microM. DCG IV (1 microM) had no effect on inhibitory postsynaptic currents mediated by GABA. DCG IV-induced inhibition of EPSCs was reversed by the selective group II mGluR antagonist LY 341495 (100 nM) and mimicked by another selective group II agonist (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I). Inhibition of EPSC amplitude by DCG IV and L-CCG-I was associated with an increase in the paired-pulse ratio of EPSCs. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (2 microM) reduced the inhibitory effect of DCG IV on EPSCs. However, the response to DCG IV was not affected by the protein kinase A (PKA) activator forskolin (20 microM), by the adenylyl cyclase inhibitor MDL 12230A (20 microM), or by the phosphodiesterase inhibitor Ro 20-1724 (50 microM). DCG IV-induced inhibition of EPSCs was reduced by the non-selective protein kinase inhibitors H-7 (100 microM), H-8 (50 microM) and HA-1004 (100 microM). These results suggest that group II mGluR stimulation acts presynaptically to inhibit glutamate release by a PKC-dependent mechanism in the subthalamic nucleus.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; 2-Amino-5-phosphonovalerate; 4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; 6-Cyano-7-nitroquinoxaline-2,3-dione; Adenylyl Cyclase Inhibitors; Amino Acids; Amino Acids, Dicarboxylic; Animals; Colforsin; Cyclopropanes; Electric Stimulation; Electrophysiology; Enzyme Inhibitors; Excitatory Postsynaptic Potentials; Glycine; Imines; In Vitro Techniques; Isoquinolines; Male; Picrotoxin; Protein Kinase C; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Subthalamic Nucleus; Sulfonamides; Synaptic Transmission; Tetradecanoylphorbol Acetate; Xanthenes

Molecular cloning has revealed the existence of at least eight subtypes of metabotropic glutamate receptors (mGluRs). We examined the effect of (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV), a selective agonist of the mGluR 2/3 subtype, on excitotoxicity in mouse cortical cell cultures. Addition of DCG-IV to the exposure medium partially attenuated the rapidly triggered excitotoxic death induced by a 5 min exposure to 200 microM NMDA. This neuroprotective effect was reversed by coapplication of alpha-methyl-4-carboxyphenylglycine (MCPG), an antagonist of mGluRs, by pertussis toxin pretreatment and also by preincubation with dibutyryl cAMP, a stable analogue of cAMP. These results suggest that the activation of mGluR 2/3 is neuroprotective in our system. However, DCG-IV did not attenuate the slowly triggered neuronal death induced by 24 h exposure to low concentrations of NMDA, alpha-amino-1,3-cyclopentanedicarboxylic acid (AMPA) or kainate. The failure of DCG-IV to block slowly triggered NMDA neurotoxicity is likely due to weak NMDA agonist activity, as demonstrated in whole-cell recording.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Bucladesine; Cell Death; Cell Survival; Cells, Cultured; Cerebral Cortex; Cyclic AMP; Cyclopropanes; Glycine; Kainic Acid; Membrane Potentials; Mice; N-Methylaspartate; Neurons; Neurotoxins; Pertussis Toxin; Receptors, Metabotropic Glutamate; Virulence Factors, Bordetella

The electrophysiological action of (2S,1'R;2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV) on the NMDA receptor was investigated with the help of concentration-jump experiments on freshly dissociated hippocampal CA1 and CA3 neurons of rats. Inward currents elicited by a pulse of DCG-IV were insensitive to 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and could be blocked by D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5) and magnesium and enhanced by glycine. The substance displayed cross-desensitization with NMDA but not with kainate or (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Dose-response curves showed that DCG-IV was weaker than NMDA but more potent than glutamate in eliciting agonist-gated currents. From these data we conclude that DCG-IV has to be used with caution as a tool for the investigation of metabotropic glutamate receptors.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cyclopropanes; Dose-Response Relationship, Drug; Drug Interactions; Electrophysiology; Glycine; Hippocampus; Kainic Acid; Magnesium; N-Methylaspartate; Neurons; Patch-Clamp Techniques; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Stereoisomerism