6-cyano-7-nitroquinoxaline-2-3-dione and 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic-acid

We obtained field, K(+) selective and "sharp" intracellular recordings from the rat entorhinal (EC) and perirhinal (PC) cortices in an in vitro brain slice preparation to identify the events occurring at interictal-to-ictal transition during 4-aminopyridine application. Field recordings revealed interictal- (duration: 1.1 to 2.2s) and ictal-like (duration: 31 to 103s) activity occurring synchronously in EC and PC; in addition, interictal spiking in PC increased in frequency shortly before the onset of ictal oscillatory activity thus resembling the hypersynchronous seizure onset seen in epileptic patients and in in vivo animal models. Intracellular recordings with K-acetate+QX314-filled pipettes in PC principal cells showed that spikes at ictal onset had post-burst hyperpolarizations (presumably mediated by postsynaptic GABAA receptors), which gradually decreased in amplitude. This trend was associated with a progressive positive shift of the post-burst hyperpolarization reversal potential. Finally, the transient elevations in [K(+)]o (up to 4.4mM from a base line of 3.2mM) - which occurred with the interictal events in PC - progressively increased (up to 7.3mM) with the spike immediately preceding ictal onset. Our findings indicate that hypersynchronous seizure onset in rat PC is caused by dynamic weakening of GABAA receptor signaling presumably resulting from [K(+)]o accumulation.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Cations, Monovalent; Cerebral Cortex; Excitatory Amino Acid Antagonists; GABA Antagonists; Neurons; Periodicity; Phosphinic Acids; Picrotoxin; Piperazines; Potassium; Propanolamines; Rats, Sprague-Dawley; Receptors, GABA-A; Receptors, GABA-B; Receptors, N-Methyl-D-Aspartate; Seizures; Tissue Culture Techniques

Previous studies have reported subsets of medullary raphé neurons that are either stimulated or inhibited by CO2/pH in vitro, in situ, and in vivo. We tested the hypothesis that medullary raphé CO2-inhibited neurons are GABAergic. Extracellular recordings in unanesthetized juvenile in situ rat preparations showed reversible hypercapnia-induced suppression of 19% (63/323) of medullary raphé neurons, and this suppression persisted after antagonism of NMDA, AMPA/kainate, and GABAA receptors. We stained a subset of CO2-inhibited cells and found that most (11/12) had glutamic acid decarboxylase 67 immunoreactivity (GAD67-ir). These data indicate that the majority of acidosis-inhibited medullary raphé neurons are GABAergic, and that their chemosensitivity is independent of major fast synaptic inputs. Thus, CO2-sensitive GABAergic neurons may play a role in central CO2/pH chemoreception.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Animals, Newborn; Bicuculline; Biotin; Carbon Dioxide; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; GABA Antagonists; GABAergic Neurons; gamma-Aminobutyric Acid; Glutamate Decarboxylase; In Vitro Techniques; Male; Midbrain Raphe Nuclei; Patch-Clamp Techniques; Piperazines; Rats; Rats, Sprague-Dawley; Tryptophan Hydroxylase

Dopamine is critical for higher neural processes and modifying the activity of the prefrontal cortex (PFC). However, the mechanism of dopamine contribution to the modification of neural representation is unclear. Using in vivo two-photon population Ca(2+) imaging in awake mice, this study investigated how neural representation of visual input to PFC neurons is regulated by dopamine. Phasic stimulation of dopaminergic neurons in the ventral tegmental area (VTA) evoked prolonged Ca(2+) transients, lasting ~30 s in layer 2/3 neurons of the PFC, which are regulated by a dopamine D1 receptor-dependent pathway. Furthermore, only a conditioning protocol with visual sensory input applied 0.5 s before the VTA dopaminergic input could evoke enhanced Ca(2+) transients and increased pattern similarity (or establish a neural representation) of PFC neurons to the same sensory input. By increasing both the level of neuronal response and pattern similarity, dopaminergic input may establish robust and reliable cortical representation.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Benzazepines; Calcium; Dopamine; Dopamine Antagonists; Dopaminergic Neurons; Electric Stimulation; Evoked Potentials, Visual; Mice; Mice, Inbred C57BL; Neural Pathways; Piperazines; Prefrontal Cortex; Receptors, Dopamine D1; Salicylamides; Stereotaxic Techniques; Synaptic Transmission; Ventral Tegmental Area; Wakefulness

Fragile X syndrome is a neurodevelopmental condition caused by the transcriptional silencing of the fragile X mental retardation 1 (FMR1) gene. The Fmr1 knockout (KO) mouse exhibits age-dependent deficits in long term potentiation (LTP) at association (ASSN) synapses in anterior piriform cortex (APC). To investigate the mechanisms for this, whole-cell voltage-clamp recordings of ASSN stimulation-evoked synaptic currents were made in APC of slices from adult Fmr1-KO and wild-type (WT) mice, using the competitive N-methyl-D-aspartate (NMDA) receptor antagonist, CPP, to distinguish currents mediated by NMDA and AMPA receptors. NMDA/AMPA current ratios were lower in Fmr1-KO mice than in WT mice, at ages ranging from 3-18months. Since amplitude and frequency of miniature excitatory postsynaptic currents (mEPSCs) mediated by AMPA receptors were no different in Fmr1-KO and WT mice at these ages, the results suggest that NMDA receptor-mediated currents are selectively reduced in Fmr1-KO mice. Analyses of voltage-dependence and decay kinetics of NMDA receptor-mediated currents did not reveal differences between Fmr1-KO and WT mice, suggesting that reduced NMDA currents in Fmr1-KO mice are due to fewer synaptic receptors rather than differences in receptor subunit composition. Reduced NMDA receptor signaling may help to explain the LTP deficit seen at APC ASSN synapses in Fmr1-KO mice at 6-18months of age, but does not explain normal LTP at these synapses in mice 3-6months old. Evoked currents and mEPSCs were also examined in senescent Fmr1-KO and WT mice at 24-28months of age. NMDA/AMPA ratios were similar in senescent WT and Fmr1-KO mice, due to a decrease in the ratio in the WT mice, without significant change in AMPA receptor-mediated mEPSCs.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Age Factors; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Bicuculline; Biophysics; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Fragile X Mental Retardation Protein; GABA-A Receptor Antagonists; In Vitro Techniques; Mice; Mice, Inbred C57BL; Mice, Knockout; N-Methylaspartate; Patch-Clamp Techniques; Piperazines; Prefrontal Cortex; Receptors, N-Methyl-D-Aspartate; Sodium Channel Blockers; Synapses; Tetrodotoxin

Reactive oxygen species (ROS) modulate neuronal excitability. In the present study we examined the effects of hydrogen peroxide (H(2)O(2)), a well established ROS, on neuronal activity from two neonatal mouse brain regions, i.e., the pre-Bötzinger complex (preBötC) within the ventral respiratory column (VRC) and the CA1 area of the hippocampus. In the preBötC, 2.2 mM H(2)O(2) evoked a transient depression followed by augmentation of neuronal activity. The iron chelator deferoxamine (500 μM) did not prevent H(2)O(2)-mediated neuronal augmentation but prevented the initial depression. Combined application of Fe(2+) and H(2)O(2) only caused depression of the preBötC rhythm. In contrast, H(2)O(2) suppressed neuronal activity in the CA1 region, and this effect was accentuated by coapplication of Fe(2+) and H(2)O(2), suggesting that hydroxyl radical generated by Fenton reaction mediates the effects of H(2)O(2) on CA1 neuronal activity. Malondialdehyde (MDA) levels were monitored as an index of lipid peroxidation in H(2)O(2)-treated preBötC and CA1 areas. MDA levels were unaltered in H(2)O(2)-treated preBötC, whereas MDA levels were markedly elevated in the CA1 region. These findings suggest that 1) exogenous administration of H(2)O(2) exerts differential effects on neuronal activities of preBötC versus CA1 neuronal populations and 2) H(2)O(2) is a potent modulator of respiratory rhythmogenesis from the preBötC without affecting global oxidative status.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Animals, Newborn; Biophysics; Deferoxamine; Dose-Response Relationship, Drug; Drug Interactions; Electric Stimulation; Excitatory Amino Acid Antagonists; Ferrous Compounds; GABA Antagonists; Hippocampus; Hydrogen Peroxide; In Vitro Techniques; Lipid Peroxidation; Malondialdehyde; Mice; Neurons; Oxidants; Patch-Clamp Techniques; Picrotoxin; Piperazines; Respiratory Center; Siderophores

In adult mice, classical conditioning in which whisker stimulation is paired with an electric shock to the tail results in a decrease in the frequency of head movements, induces expansion of the cortical representation of stimulated vibrissae and enhances inhibitory synaptic interactions within the 'trained' barrels. We investigated whether such a simple associative learning paradigm also induced changes in neuronal excitability. Using whole-cell recordings from ex vivo slices of the barrel cortex we found that layer IV excitatory cells located in the cortical representation of the 'trained' row of vibrissae had a higher frequency of spikes recorded at threshold potential than neurons from the 'untrained' row and than cells from control animals. Additionally, excitatory cells within the 'trained' barrels were characterized by increased gain of the input-output function, lower amplitudes of fast after-hyperpolarization and decreased effect of blocking of BK channels by iberiotoxin. These findings provide new insight into the possible mechanism for enhanced intrinsic excitability of layer IV excitatory neurons. In contrast, the fast spiking inhibitory cells recorded in the same barrels did not change their intrinsic excitability after the conditioning procedure. The increased excitability of excitatory neurons within the 'trained' barrels may represent the counterpart of homeostatic plasticity, which parallels enhanced synaptic inhibition described previously. Together, the two mechanisms would contribute to increase the input selectivity within the conditioned cortical network.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Bicuculline; Conditioning, Classical; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; Large-Conductance Calcium-Activated Potassium Channels; Male; Mice; Mice, Inbred C57BL; Neurons; Patch-Clamp Techniques; Peptides; Piperazines; Potassium Channel Blockers; Somatosensory Cortex

The anterior cingulate cortex (ACC)--which plays a role in pain, emotions and behavior--can generate epileptic seizures. To date, little is known on the neuronal mechanisms leading to epileptiform synchronization in this structure. Therefore, we investigated the role of excitatory and inhibitory synaptic transmission in epileptiform activity in this cortical area. In addition, since the ACC presents with a high density of opioid receptors, we studied the effect of opioid agonism on epileptiform synchronization in this brain region.. We used field and intracellular recordings in conjunction with pharmacological manipulations to characterize the epileptiform activity generated by the rat ACC in a brain slice preparation.. Bath-application of the convulsant 4-aminopyridine (4AP, 50 microM) induced both brief and prolonged periods of epileptiform synchronization resembling interictal- and ictal-like discharges, respectively. Interictal events could occur more frequently before the onset of ictal activity that was contributed by N-methyl-D-aspartate (NMDA) receptors. Mu-opioid receptor activation abolished 4AP-induced ictal events and markedly reduced the occurrence of the pharmacologically isolated GABAergic synchronous potentials. Ictal discharges were replaced by interictal events during GABAergic antagonism; this GABA-independent activity was influenced by subsequent mu-opioid agonist application.. Our results indicate that both glutamatergic and GABAergic signaling contribute to epileptiform synchronization leading to the generation of electrographic ictal events in the ACC. In addition, mu-opioid receptors appear to modulate both excitatory and inhibitory mechanisms, thus influencing epileptiform synchronization in the ACC.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Anticonvulsants; Cortical Synchronization; Electroencephalography; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Epilepsies, Partial; Evoked Potentials; GABA Antagonists; Gyrus Cinguli; In Vitro Techniques; Male; Membrane Potentials; Neural Inhibition; Neurons; Piperazines; Potassium Channel Blockers; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, GABA-A; Receptors, GABA-B; Receptors, Glutamate; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Receptors, Opioid, mu; Synaptic Transmission

The subplate plays an important role in forming neuronal connections during early cortical development. We characterized by the use of whole-cell and cell-attached patch-clamp recordings in coronal brain slices from newborn mice (postnatal day [P] 0-3) the functional properties of two major pathways onto subplate neurons (SPn), the thalamocortical and the intra-subplate synaptic input. The two afferent pathways were stimulated extracellularly with bipolar electrodes placed in the thalamus and the subplate, respectively. Synaptically evoked and pharmacologically isolated N-methyl-d-aspartate receptor (NMDAR) -mediated responses with an onset latency of approximately 6 ms could be reliably recorded in P0-3 SPn. Whereas the intra-subplate input revealed a pronounced facilitation using paired pulse stimulation at 60-120 ms or repetitive activation at 10-40 Hz, the thalamocortical input was either stable or markedly suppressed under these conditions. Single cell reverse transcription PCR revealed the expression of the NR2A, B and D subunit in all investigated SPn. The intra-subplate and the thalamocortical synaptic input did not differ in their sensitivity to NVP-AAM077 or ifenprodil, indicating that both synaptic inputs have a similar NR2A/2B subunit composition. At P0, NMDAR-mediated synaptic inputs arising from the thalamus were significantly larger as compared with the intra-subplate input. This difference could no longer be detected in P2-3 SPn, indicating an input-specific developmental regulation during the first Ps. Our data indicate that the thalamocortical and intra-subplate synaptic input onto P0-3 SPn differs in functional, molecular and developmental properties. The intra-subplate synaptic input shows more mature functional properties and sustains high stimulation frequencies, thereby promoting the immature thalamocortical input to the developing neocortical circuit.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Age Factors; Animals; Animals, Newborn; Cerebral Cortex; Dose-Response Relationship, Radiation; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; In Vitro Techniques; Mice; Neural Pathways; Neurons; Patch-Clamp Techniques; Piperazines; Receptors, N-Methyl-D-Aspartate; Synapses; Thalamus

The sulphur-containing amino acid homocysteic acid (HCA) is present in and released in vitro from nervous tissue and is a potent neuronal excitant, predominantly activating N-methyl-d-aspartate (NMDA) receptors. However, HCA is localised not in neurones but in glial cells [Eur J Neurosci 3 (1991) 1370], and we have shown that it is released from astrocytes in culture upon glutamate receptor activation [Neuroscience 124 (2004) 377]. We now report the in vivo release of HCA from ventrobasal (VB) thalamus following natural stimulation of somatosensory afferents arising from the facial vibrissae of the rat. Simultaneously with multi-unit recording, [35S]-methionine, a HCA precursor, was perfused through a push-pull cannula in VB thalamus of anaesthetized rats. Perfusates were collected before, during and after 4 min stimulation of the vibrissal afferents with an air jet. A marked release of radiolabeled HCA was observed during and after the stimulation. Furthermore, the beta-adrenoreceptor agonist isoproterenol, which is known to evoke HCA release from glia in vitro, was found to increase the efflux of HCA in the perfusate in vivo. In separate experiments, the excitatory actions of iontophoretically applied HCA on VB neurones were inhibited by the NMDA receptor antagonist CPP, but not by the non-NMDA antagonist CNQX. These results suggest a possible "gliotransmitter" role for HCA in VB thalamus. The release of HCA from glia might exert a direct response or modulate responses to other neurotransmitters in postsynaptic neurons, thus enhancing excitatory processes.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Brain Chemistry; Chromatography, High Pressure Liquid; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Homocysteine; Iontophoresis; Kainic Acid; Male; Methionine; N-Methylaspartate; Neuroglia; Physical Stimulation; Piperazines; Rats; Rats, Wistar; Sulfur Isotopes; Synaptic Transmission; Thalamus; Vibrissae

The effects of the P2 receptor ligands 2-methylthio ATP (2-MeSATP; 10 pmol)--as a non-specific agonist--and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 10 pmol)--as a non-selective antagonist--after bilateral intra-accumbens injection on the locomotor response were investigated in an open field situation. The P2 receptor-mediated effects on the pattern of locomotor activity were compared with the effects caused by the dopamine D2-like receptor agonist quinpirole (10 pmol) and by the combination of the N-methyl-D-aspartate (NMDA) receptor antagonist (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP; 10 pmol) with the alpha-amino-3-hydro-5-methyl-4-isoxazolpropionic acid (AMPA) and kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 30 pmol). The intra-accumbens injection of all tested compounds elicited an increase in the locomotor activity over a test period of 20 min when compared with the controls. No statistically significant differences could be evaluated between the different drug-treated groups. However, a more detailed analysis--using further behavioural parameters such as the number of movement direction changes, the effective running time and the running speed--revealed two basically different patterns of locomotor activity. The locomotor response induced by the injection of 2-MeSATP or quinpirole was characterised by a continuous and consistent locomotion, whereas the enhanced locomotor activity elicited by PPADS or CPP/CNQX was determined by an increased running speed accompanied by more disruptions and more changes of movement direction. The coadministration of 2-MeSATP and quinpirole led to an enhancement of locomotor activity in a limited post-treatment interval. The effects of both compounds could be abolished by the pre-treatment with the D2/D3 receptor antagonist sulpiride (100 pmol). Coadministration of PPADS and CPP/CNQX caused additive effects suggesting that the pathway mediated by P2 and ionotrophic glutamate receptors is different. The stimulation of P2 receptors in the nucleus accumbens (NAc) modulates the locomotion in the direction to be to be longer lasting, more consistent and more goal directed.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Adenosine Triphosphate; Animals; Behavior, Animal; Dopamine Agonists; Dopamine Antagonists; Drug Interactions; Excitatory Amino Acid Antagonists; Locomotion; Male; Nucleus Accumbens; Piperazines; Platelet Aggregation Inhibitors; Purinergic P2 Receptor Agonists; Pyridoxal Phosphate; Quinpirole; Rats; Rats, Wistar; Receptors, AMPA; Receptors, Dopamine D2; Receptors, Glutamate; Receptors, Purinergic P2; Sulpiride; Thionucleotides; Time Factors

1. Various neurotransmitters in the brain regulate gastric acid secretion. Previously, we reported that the central injection of kappa-opioid receptor agonists stimulated this secretion in rats. Although the existence of kappa(1)-kappa(3)-opioid receptor subtypes has been proposed, the character is not defined. We investigated the interactions between kappa-opioid receptor subtypes and glutamate, gamma-amino-butyric acid (GABA) or 5-hydroxy tryptamine (5-HT) receptors in the rat brain. 2. Gastric acid secretion induced by the injection of U69593 (8.41 nmol, a putative kappa(1)-opioid receptor agonist) into the lateral cerebroventricle was completely inhibited by the central injection of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10.9 nmol, an antagonist for non-N-methyl-D-aspartate (non-NMDA) receptors) and by bicuculline infusion (222 micro g kg(-1) per 10 min, i.v., GABA(A) receptor antagonist). The secretion induced by bremazocine (8.52 nmol, a putative kappa(2)-opioid receptor agonist) was inhibited by bicuculline infusion, but not by CNQX. The secretion induced by naloxone benzoylhydrazone (224 nmol, a putative kappa(3)-opioid receptor agonist) was slightly and partially inhibited by CNQX and bicuculline. 3. Treatment with CNQX and bicuculline inhibited gastric acid secretion induced by the injection of dynorphin A-(1-17) into the lateral, but not the fourth, cerebroventricle. Antagonists for NMDA, GABA(B) and 5-HT(2/1C) receptors did not inhibit the secretions by kappa-opioid receptor agonists. 4. In rat brain regions close to the lateral cerebroventricle, kappa-opioid receptor systems (kappa(1)>kappa(3)>>kappa(2)) are regulated by the non-NMDA type of glutamate receptor system, and kappa(1)- and kappa(2)-opioid receptor systems are regulated by the GABA(A) receptor system. The present findings show pharmacological evidence for kappa-opioid receptor subtypes that regulate gastric acid secretion in the rat brain.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Baclofen; Benzeneacetamides; Benzomorphans; Bicuculline; Brain; Dynorphins; gamma-Aminobutyric Acid; Gastric Acid; Injections, Intraventricular; Ketanserin; Male; Perfusion; Piperazines; Pyrrolidines; Rats; Rats, Wistar; Receptors, GABA-A; Receptors, Glutamate; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, kappa; Receptors, Serotonin; Stomach

The functional properties of spontaneous, glutamatergic EPSCs and non-NMDA receptors in AII amacrine cells were studied in whole cells and patches from slices of the rat retina using single and dual electrode voltage clamp recording. Pharmacological analysis verified that the EPSCs (Erev approximately 0 mV) were mediated exclusively by AMPA-type receptors. EPSCs displayed a wide range of waveforms, ranging from simple monophasic events to more complex multiphasic events. Amplitude distributions of EPSCs were moderately skewed towards larger amplitudes (modal peak 23 pA). Interevent interval histograms were best fitted with a double exponential function. Monophasic, monotonically rising EPSCs displayed very fast kinetics with an average 10-90 % rise time of approximately 340 micro s and a decay phase well fitted by a single exponential (taudecay approximately 760 micro s). The specific AMPA receptor modulator cyclothiazide markedly slowed the decay phase of spontaneous EPSCs (taudecay approximately 3 ms). An increase in temperature decreased both 10-90 % rise time and taudecay with Q10 values of 1.3 and 1.5, respectively. The decay kinetics were slower at positive membrane potentials compared to negative membrane potentials (205 mV/e-fold change in taudecay). Step depolarization of individual presynaptic rod bipolar cells or OFF-cone bipolar cells evoked transient, CNQX-sensitive responses in AII amacrine cells with average peak amplitudes of approximately 330 pA. Ultrafast application of brief (approximately 1 ms) or long (approximately 500 ms) pulses of glutamate to outside-out patches evoked strongly desensitizing responses with very fast deactivation and desensitization kinetics, well fitted by single (taudecay approximately 1.1 ms) and double exponential (tau1 approximately 3.5 ms; tau2 approximately 21 ms) functions, respectively. Double-pulse experiments indicated fast recovery from desensitization (tau approximately 12.4 ms). Our results indicate that spontaneous, AMPA receptor-mediated EPSCs in AII amacrine cells have very fast, voltage-dependent kinetics that can be well accounted for by the kinetic properties of the AMPA receptors themselves

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Algorithms; Amacrine Cells; Animals; Benzodiazepines; Electrophysiology; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glutamates; In Vitro Techniques; Kinetics; Membrane Potentials; Patch-Clamp Techniques; Piperazines; Presynaptic Terminals; Rats; Receptors, AMPA; Receptors, Glutamate; Retinal Rod Photoreceptor Cells; Synapses; Tetrodotoxin

The synaptic mechanisms underlying excitation in the rat's central nucleus of the inferior colliculus (ICC) were examined by making whole-cell patch clamp recordings in brain slice preparations of the auditory midbrain. Responses were elicited by current pulse stimulation of the lateral lemniscus and recordings were made in ICC using either current clamp or voltage clamp methods. The excitatory postsynaptic responses in either current or voltage clamp mode consisted of two distinct components, an early component that could be blocked by bath application of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), and a later component that could be blocked by application of the N-methyl-D-aspartate (NMDA) receptor antagonists, (+/-)-2-amino-5-phosphonovaleric acid (APV) or (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP). Both AMPA and NMDA receptor-mediated responses were present at resting potential and could be isolated pharmacologically by application of receptor antagonists. Voltage clamp experiments revealed that the NMDA receptor-mediated current was voltage-dependent and increased in magnitude as the cell membrane was depolarized. This NMDA receptor-mediated response was enhanced at resting potential when Mg(2+) was eliminated from the bath solution. The ratio of response amplitudes associated with the late and early components, an estimate of the relative contribution of NMDA and AMPA receptor types, changed with age. There was a progressive decline in the ratio between 9 and 13 days of age, but no further reduction between days 13 and 16. The data show that both AMPA and NMDA receptors are important for determining excitatory responses in the ICC and that both receptor types probably play a role in auditory processing after the onset of hearing.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Aging; Animals; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; In Vitro Techniques; Inferior Colliculi; Magnesium; Membrane Potentials; Patch-Clamp Techniques; Piperazines; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synapses

Previous research has demonstrated that intrathecal i.t. morphine in a dose of 60.0 nmol into the spinal subarachnoid space of mice can evoke nociceptive behavioral responses consisting of a severe hindlimb scratching directed toward the flank followed by biting/licking of the hindpaw. The present study was undertaken to examine the involvement of spinal N-methyl-D-aspartate (NMDA) and opioid receptors on the behavioral responses evoked by high-dose i.t. morphine. Pretreatment with naloxone, an opioid receptor antagonist (1.0 and 4.0 mg/kg, s.c.), failed to reverse the morphine-evoked behavioral response, suggesting that the morphine effect is not mediated through the opioid receptors in the spinal cord. The morphine-induced behavior was dose-dependently inhibited by i.t. co-administration of the competitive NMDA receptor antagonists, D(-)-2-amino-5-phosphonovaleric acid (D-APV) (6.25-50.0 pmol) and 3-((+)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) (3.125-25.0 pmol). The characteristic behavior was also reduced by co-administration of (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5,10-imine maleate (MK-801) (74.1-250 pmol), an NMDA ion-channel blocker. Ifenprodil, a competitive antagonist of the polyamine recognition site of NMDA receptor ion channel complex, produced a dose-related inhibitory effect on the behavioral response to i.t. morphine with less potency than the competitive and non-competitive antagonists examined. High doses of (+)-HA-966, a glycine/NMDA antagonist, induced a dose-dependent inhibition of morphine-induced response. The effective dose of i.t. 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, needed to reduce the morphine-induced response, was approximately 10-fold greater than that of D-APV. These results suggest that spinal NMDA receptors, but not non-NMDA receptors, may be largely involved in elicitation of the behavioral episode following i.t. injection of morphine in mice.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Binding, Competitive; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glutamic Acid; Hindlimb; Hyperalgesia; Injections, Spinal; Male; Mice; Mice, Mutant Strains; Morphine; Naloxone; Narcotic Antagonists; Nerve Tissue Proteins; Pain Measurement; Piperazines; Piperidines; Pyrrolidinones; Reaction Time; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Spinal Cord; Subarachnoid Space

Immunocytochemical and Co(2+) uptake studies revealed that in primary cultures of rat cortical neurones, the majority of neurones are gamma-aminobutyric acid (GABA) immunopositive and can express Ca(2+)-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors. By fura-2 microfluorimetry, it was shown that the stimulation with the selective agonist (S)-AMPA (0.3-300 microM) induced a concentration-dependent but cell-variable increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) (EC(50) value 7.4 microM) in more than 80% of the medium-sized multipolar neurones studied. The AMPA-induced rise in [Ca(2+)](i) seems to be due to Ca(2+) entry through AMPA receptor channels, because the response was abolished in Ca(2+)-free solution and by AMPA receptor selective antagonists, but was not significantly influenced by cyclopiazonic acid, an inhibitor of the endoplasmatic Ca(2+)-ATPase, by selective N-methyl-D-aspartic acid (NMDA) receptor antagonists, as well as the Na(+) channel blocker tetrodotoxin and the majority of tested Ca(2+) channel blockers. In conclusion, the results indicate that the cerebral cortical neurones in culture represent mostly GABAergic interneurone-like cells and the majority of them possess Ca(2+)-permeable AMPA receptors, important for intracellular signal transduction and neuronal plasticity.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Benzodiazepines; Benzothiadiazines; Calcium; Cells, Cultured; Cerebral Cortex; Cobalt; Diazoxide; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Fluorescence; Fluorometry; Fura-2; gamma-Aminobutyric Acid; Immunohistochemistry; N-Methylaspartate; Neurons; Piperazines; Quinoxalines; Rats; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate

We examined the effects of 4-aminopyridine (4-AP) on isolated horizontal (superficial, middle and deep) rat neocortical slices in order to study laminar synchronous network behavior directly. Application of 4-AP induced spontaneous synchronized activity in all of these types of slices. In middle and deep layer slices the activities were similar to those of coronal slices, consisting of periodic short- and long-duration discharges. In superficial slices distinct spontaneous rhythmic multiphasic burst discharges were induced. Ionotropic glutamate receptor antagonists blocked the 4-AP-induced synchronous activities in middle and deep layer slices, but those in superficial slices persisted. The GABA(A) receptor antagonist picrotoxin suppressed this spontaneous synchronous activity resistant to 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (a NMDA receptor antagonist) and 6-cyano-7-nitroquinoxaline-2,3-dione (a non-NMDA receptor antagonist), in superficial slices, leaving small, slow spontaneous events. In superficial slices with intact excitatory amino acid transmission, picrotoxin attenuated the 4-AP-induced spontaneous synchronous discharges, even in this highly convulsant environment. By contrast, conventional coronal slices showed robust spontaneous epileptiform discharges under these circumstances. In intact coronal slices focal 4-AP application in superficial layers induced spontaneous inhibitory GABAergic events, while delivery into deep layers led to epileptiform discharges. From these results we conclude that: (1) 4-AP-induced population discharges are driven by glutamatergic transmission in middle and deep layer horizontal slices, and by GABAergic transmission in superficial layers; (2) only superficial layers are capable of supporting synchronized GABAergic activity independent of excitatory amino acid transmission; (3) superficial layers do not sustain epileptiform activity in the absence of deep layer neurons; and (4) synchronized superficial networks can inhibit deep layer neuronal activity.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Electrophysiology; Excitatory Amino Acid Antagonists; GABA Antagonists; In Vitro Techniques; Intracellular Membranes; Neocortex; Nerve Net; Picrotoxin; Piperazines; Rats; Rats, Sprague-Dawley

The convulsant 4-aminopyridine (4AP) facilitates the synchronous firing of interneurons in the hippocampus, eliciting giant inhibitory postsynaptic potentials (IPSPs) in CA3 pyramidal cells. We used the gap junction blocker carbenoxolone to investigate the role of electrotonic coupling in both the initiation and the maintenance of 4AP-facilitated inhibitory circuit oscillations. Carbenoxolone abolished all synchronized IPSPs in CA3 cells elicited by 4AP in the presence of ionotropic glutamate receptor blockers. Carbenoxolone also blocked the isolated synchronized GABA(B) IPSPs generated in CA3 cells by a subpopulation of interneurons. These data confirm that: (1) the interneurons producing GABA(B) responses in CA3 cells are electrotonically coupled, and (2) gap junctions among interneurons are essential for initiating synchronized interneuron oscillatory firing in 4AP.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Bicuculline; Carbenoxolone; Convulsants; Evoked Potentials; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; Gap Junctions; Guinea Pigs; Hippocampus; Interneurons; Piperazines; Pyramidal Cells; Receptors, AMPA; Receptors, GABA-B; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission

Low-frequency network oscillations occur in several areas of the limbic system where they contribute to synaptic plasticity and mnemonic functions that are in turn modulated by cholinergic mechanisms. Here we used slices of the rat subiculum (a limbic area involved in cognitive functions) to establish how network and single neuron (intrinsic) membrane mechanisms participate to the rhythmic oscillations elicited by the cholinergic agent carbachol (CCh, 50-100 microM). We have found that CCh-induced network oscillations (intraoscillatory frequency = 5-16 Hz) are abolished by an antagonist of non-N-methyl-D-aspartate (NMDA) glutamatergic receptors (n = 6 slices) but persist during blockade of GABA receptors (n = 16). In addition, during application of glutamate and GABA receptor antagonists, single subicular cells generate burst oscillations at 2.1-6.8 Hz when depolarized with steady current injection. These intrinsic burst oscillations disappear during application of a Ca(2+) channel blocker (n = 6 cells), intracellular Ca(2+) chelation (n = 6), or replacement of extracellular Na(+) (n = 4) but persist in recordings made with electrodes containing a blocker of voltage-gated Na(+) channels (n = 7). These procedures cause similar effects on CCh-induced depolarizing plateau potentials that are contributed by a Ca(2+)-activated nonselective cationic conductance (I(CAN)). Network and intrinsic oscillations along with depolarizing plateau potentials were abolished by the muscarinic receptor antagonist atropine. In conclusion, our findings demonstrate that low-frequency oscillations in the rat subiculum rely on the muscarinic receptor-dependent activation of an intrinsic oscillatory mechanism that is presumably contributed by I(CAN) and are integrated within the network via non-NMDA receptor-mediated transmission.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Atropine; Bicuculline; Carbachol; Chelating Agents; Cholinergic Agonists; Egtazic Acid; Excitatory Amino Acid Antagonists; GABA Antagonists; Hippocampus; Male; Muscarinic Antagonists; Neural Pathways; Organophosphorus Compounds; Periodicity; Picrotoxin; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, Glutamate

Activity-dependent synaptic plasticity triggered by N-methyl-d-aspartate (NMDA) receptor activation is a fundamental property of many glutamatergic synapses and may be critical for the shaping and refinement of the structural and functional properties of neuronal circuits during early postnatal development. Using a combined morphological and electrophysiological approach, we showed that chronic blockade of NMDA receptors in hippocampal slice cultures during the first two weeks of postnatal development leads to a substantial increase in synapse number and results in a more complex dendritic arborization of CA1 pyramidal cells. Thus, the development of excitatory circuitry in the hippocampus is determined by two opposing processes: NMDA receptor-independent synapse formation and NMDA receptor-dependent attenuation of synaptogenesis.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Animals, Newborn; Cell Surface Extensions; Cells, Cultured; Dendrites; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Hippocampus; Histocytochemistry; In Vitro Techniques; Ion Channels; Lysine; Microscopy, Confocal; Patch-Clamp Techniques; Piperazines; Pyramidal Cells; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synapses

The antiepileptic drug, gamma-vinyl GABA (GVG, vigabatrin), is an irreversible inhibitor of GABA-transaminase, the enzyme responsible for the breakdown of GABA. In hippocampal slices prepared from rats pretreated with either an anticonvulsant dose of GVG (1500 mg/kg) or saline, electrophysiological recordings were performed in order to examine the effects of GVG pretreatment on GABAergic neurotransmission. Although GVG had no effect on the effectiveness of GABA-mediated inhibition when elicited by a single stimulus, it reversed the activity-dependent depression of inhibition which is typically observed when inhibitory pathways are activated repetitively by a train of stimuli delivered at low frequency. Similarly, GVG pretreatment prevented the progressive decline in the amplitude of monosynaptic inhibitory postsynaptic potentials (IPSPs) during low-frequency stimulation of inhibitory interneurons. Thus, in slices from GVG pretreated rats, the amplitudes of both the fast and slow components of the last of a series of IPSPs evoked by a 5 Hz, 4 s train were maintained at 91.5 +/- 6.6% and 87.7 +/- 6.5%, respectively, compared to 61.1 +/- 3.9% and 57.1 +/- 5.0% in control slices. Finally, in slices from GVG pretreated rats, we observed a reduction in the ability of the GABA(B) receptor agonist, baclofen, to decrease the amplitude of monosynaptic inhibitory postsynaptic currents. These results suggest that GVG may produce its frequency-dependent actions by reducing the function of release regulating presynaptic GABA(B) autoreceptors. The frequency-dependent reinforcement of inhibition by GVG may importantly contribute to the anticonvulsant effectiveness of this compound.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Anticonvulsants; Electric Stimulation; Evoked Potentials; gamma-Aminobutyric Acid; Hippocampus; In Vitro Techniques; Interneurons; Male; Piperazines; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Synapses; Synaptic Transmission; Vigabatrin

Binaural responses of single neurons in the rat's central nucleus of the inferior colliculus (ICC) were recorded before and after local injection of excitatory amino acid receptor antagonists (either 1,2, 3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide disodium [NBQX], (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid [CPP], 6-cyano-7-nitroquinoxaline-2,3-dione [CNQX], or (+/-)-2amino-5-phosphonovaleric acid [APV]) into the dorsal nucleus of the lateral lemniscus (DNLL). Responses were evoked by clicks delivered separately to the two ears at interaural time delays between -1.0 and +30 ms (positive values referring to ipsilateral leading contralateral click pairs). The neurons in our sample were excited by contralateral stimulation and inhibited by ipsilateral stimulation, and the probability of action potentials was reduced as the ipsilateral stimulus was advanced. Binaural inhibition resulted in response suppression that lasted up to 30 ms. Injection of excitatory amino acid antagonists into the DNLL contralateral to the recording site reduced the strength of binaural inhibition in the ICC. The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist NBQX preferentially affected responses at small interaural time intervals (0-1.0 ms), whereas the N-methyl-D-aspartate (NMDA) antagonist CPP preferentially affected responses at longer intervals (1-30 ms). Both CNQX and APV produced a release from binaural inhibition, but neither drug was selective for specific intervals. The data support the idea that binaural inhibition in the rat ICC is influenced by both AMPA and NMDA receptor-mediated excitatory events in the contralateral DNLL. The results suggest that the AMPA receptors contribute selectively to the initial component of binaural inhibition and the NMDA receptors to a longer lasting component.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Acoustic Stimulation; Animals; Cochlear Nucleus; Excitatory Amino Acid Antagonists; Functional Laterality; Hearing; In Vitro Techniques; Inferior Colliculi; Male; Piperazines; Pons; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Time Factors

Cultures of primary neurons or thin brain slices are typically prepared from immature animals. We introduce a method to prepare hippocampal slice cultures from mature rats aged 20-30 days. Mature slice cultures retain hippocampal cytoarchitecture and synaptic connections up to 3 months in vitro. Spontaneous epileptiform activity is rarely observed suggesting long-term retention of normal neuronal excitability and of excitatory and inhibitory synaptic networks. Picrotoxin, a GABAergic Cl(-) channel antagonist, induced characteristic interictal-like bursts that originated in the CA3 region, but not in the CA1 region. These data suggest that mature slice cultures displayed long-term retention of GABAergic inhibitory synapses that effectively suppressed synchronized burst activity via recurrent excitatory synapses of CA3 pyramidal cells. Mature slice cultures lack the reactive synaptogenesis, spontaneous epileptiform activity, and short life span that limit the use of slice cultures isolated from immature rats. Mature slice cultures are anticipated to be a useful addition for the in vitro study of normal and pathological hippocampal function.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Age Factors; Animals; Electrophysiology; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Hippocampus; Microscopy, Electron; Mossy Fibers, Hippocampal; Neuroglia; Neurons; Organ Culture Techniques; Piperazines; Rats; Rats, Sprague-Dawley; Time Factors

At early developmental stages, silent synapses have been commonly found in different brain areas. These synapses are called silent because they do not respond at rest but are functional at positive membrane potentials. A widely accepted interpretation is that N-methyl-d-aspartate (NMDA) but not alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are functionally expressed on the subsynaptic membrane. Here we show that, in both CA3 and CA1 hippocampal regions, AMPA-mediated synaptic responses can be detected already at early stages of postnatal development. However, some synapses appear silent because of a very low probability of glutamate release. They can be converted into functional ones by factors that enhance release probability such as paired-pulse stimulation, increasing the temperature or cyclothiazide (CTZ), a drug that blocks AMPA receptor desensitization and increases transmitter release. Conversely, conducting synapses can be switched off by increasing the frequency of stimulation. Although we cannot exclude that "latent AMPA receptors" can become functional after activity-dependent processes, our results clearly indicate that, in the neonatal hippocampus, a proportion of glutamatergic synaptic connections are presynaptically rather than postsynaptically silent.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Animals, Newborn; Benzothiadiazines; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glutamic Acid; In Vitro Techniques; Mossy Fibers, Hippocampal; Piperazines; Probability; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission; Temperature

The repeated injection of cocaine causes an increase in the capacity of a subsequent acute injection to elevate extracellular glutamate levels in the nucleus accumbens, and the present study sought to determine if the elevation in extracellular glutamate is regulated by the pairing of environmental stimuli with drug administration. Three treatment groups were injected daily for seven days with saline or cocaine (15 mg/kg, ip); 1) injection of saline in the home cage, 2) injection of cocaine in the home cage (cocaine-unpaired), and 3) injection of cocaine in the test apparatus (cocaine-paired). Three weeks following the last daily injection dialysis probes were placed into the nucleus accumbens and all rats were injected with saline followed by cocaine. Basal levels of extracellular glutamate were significantly reduced in the cocaine-paired treatment group. Moreover, only in the cocaine-paired group did the cocaine injection elevate extracellular glutamate. Repeated administration of cocaine also produces an enduring increase in the motor stimulant response to an acute cocaine injection and it was previously found that administration of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and kainic acid glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2, 3-dione inhibited the sensitized, but not the acute motor, response to cocaine. In this study it was found that the motor stimulant response elicited by cocaine was blunted by pretreatment of the nucleus accumbens with 6-cyano-7-nitroquinoxaline-2,3-dione only in animals receiving daily cocaine injections in the paired environment. In contrast, the N-methyl-D-aspartate glutamate receptor antagonist R-(-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid did not significantly affect cocaine-induced motor activity in any treatment group. These data support a hypothesis that environmental stimuli previously associated with daily cocaine administration can modulate glutamate transmission in the nucleus accumbens in a manner affecting cocaine-induced behavior.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Brain Chemistry; Cocaine; Excitatory Amino Acid Antagonists; Extracellular Space; Glutamic Acid; Male; Microdialysis; Microinjections; Neurotransmitter Agents; Nucleus Accumbens; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Stimulation, Chemical; Synaptic Transmission

Intracellular and field potential recordings were taken from the lateral nucleus of the amygdala in a rat horizontal brain slice preparation that included hippocampal formation. Pyramidal cells comprised the majority of labeled cells (77%). Electrophysiological classification based on hyperpolarizing or depolarizing afterpotentials subdivided both the pyramidal and non-pyramidal cell classes, although pyramidal cells tended to have hyperpolarizing afterpotentials (70%) and non-pyramidal cells tended to have depolarizing afterpotentials (63%). Synchronous population bursts were triggered with single extracellular stimuli in the deep layers of entorhinal cortex. These events propagated from deep layers of entorhinal cortex into the lateral nucleus of the amygdala. Latencies were consistent with a direct entorhinal to amygdala projection. Individual lateral nucleus neurons exhibited responses ranging from a long burst response that included an initial period of 200 Hz firing and a tail of gamma frequency firing lasting over 100 ms (grade 1) to an epsp with no firing (grade 4). Half of pyramidal cells responding to events initiated in entorhinal cortex were found to receive epsps strong enough to trigger firing. Only one stellate neuron fired in response to entorhinal stimulation. Excitatory postsynaptic responses included NMDA and non-NMDA receptor mediated components. We demonstrate that synchronous population events can propagate from entorhinal cortex to the lateral nucleus of the amygdala and that pyramidal neurons of the lateral nucleus are more common targets than stellate neurons. We conclude that other synchronous events such as sharp waves and interictal spikes can spread from entorhinal cortex to amygdala in the same manner.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Amygdala; Animals; Cell Size; Cortical Synchronization; Dendrites; Electric Stimulation; Entorhinal Cortex; Excitatory Amino Acid Antagonists; Male; Neural Inhibition; Neural Pathways; Neurons; Picrotoxin; Piperazines; Rats; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate

Persistent potentiations of the chemical and electrotonic components of the eighth nerve (NVIII) EPSP recorded in vivo in the goldfish reticulospinal neuron, the Mauthner cell, can be evoked by afferent tetanization or local dendritic application of an endogenous transmitter, dopamine (3-hydroxytyramine). These modifications are attributable to the activation of distinct intracellular kinase cascades. Although dopamine-evoked potentiation (DEP) is mediated by the cAMP-dependent protein kinase (PKA), tetanization most likely activates a Ca2+-dependent protein kinase via an increased intracellular Ca2+ concentration. We present evidence that the eighth nerve tetanus that induces LTP does not act by triggering dopamine release, because it is evoked in the presence of a broad spectrum of dopamine antagonists. To test for interactions between these pathways, we applied the potentiating paradigms sequentially. When dopamine was applied first, tetanization produced additional potentiation of the mixed synaptic response, but when the sequence was reversed, DEP was occluded, indicating that the synapses potentiated by the two procedures belong to the same or overlapping populations. Experiments were conducted to determine interactions between the underlying regulatory mechanisms and the level of their convergence. Inhibiting PKA does not impede tetanus-induced LTP, and chelating postsynaptic Ca2+ with BAPTA does not block DEP, indicating that the initial steps of the induction processes are independent. Pharmacological and voltage-clamp analyses indicate that the two pathways converge on functional AMPA/kainate receptors for the chemically mediated EPSP and gap junctions for the electrotonic component or at intermediaries common to both pathways. A cellular model incorporating these interactions is proposed on the basis of differential modulation of synaptic responses via receptor-protein phosphorylation.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Benzazepines; Calcium; Chelating Agents; Dopamine; Dopamine Antagonists; Egtazic Acid; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Goldfish; In Vitro Techniques; Long-Term Potentiation; Neurons, Afferent; Patch-Clamp Techniques; Piperazines; Receptors, N-Methyl-D-Aspartate; Spiperone; Synapses; Vestibulocochlear Nerve

Microdialysis experiments were used to investigate the influence of locally applied 2-methylthioadenosine 5'-triphosphate (2-MeSATP) on extracellular dopamine concentrations in the rat nucleus accumbens (NAc). 2-MeSATP (0.1, 1, 10 mM) infused via the microdialysis probe caused a concentration-dependent stimulation of dopamine release. The P2 receptor antagonists reactive blue 2 and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (30 microM each) depressed the basal release of dopamine when given alone and in addition counteracted the stimulatory effect of 2-MeSATP (1 mM). In contrast, a combination of the excitatory amino acid receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 300 microM) and 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP; 100 microM) increased the basal release of dopamine by themselves and facilitated the effect of 2-MeSATP (1 mM). The results suggest a physiologically relevant regulation of tonic dopamine release in the NAc by endogenous ATP via P2 receptors. This is due to the combination of a direct and an indirect (via glutamate release) effect of ATP on mesolimbic dopaminergic neurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Adenosine Triphosphate; Analysis of Variance; Animals; Dopamine; Excitatory Amino Acid Antagonists; Male; Microdialysis; Nucleus Accumbens; Piperazines; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate; Rats; Rats, Wistar; Thionucleotides; Triazines

Nociceptive primary afferent C-fibers express a subset of glutamate receptors that are sensitive to kainic acid. Thus, we tested the possibility that activation of these receptors alters nociception. Intraperitoneal (i.p.) injection of kainic acid induced a persistent thermal hyperalgesia, when tested using the hot plate (mice) and tail flick (mice and rats) assays, and mechanical hyperalgesia when tested using von Frey monofilaments (rats), but had no effect on acetic acid-induced chemical nociception (mice). When administered i. p., 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an (R, S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid HBr/kainate (AMPA/KA) antagonist, completely blocked hyperalgesia. When injected intrathecally (i.t.), kainic acid itself failed to induce hyperalgesia and AMPA/KA antagonists given i.t. also failed to attenuate the hyperalgesic effect of kainic acid administered i.p. , indicating that the spinal cord is not the primary site of action. Kainic acid injected subcutaneously in the back of mice decreased response latencies in the hot plate and tail flick assays, indicating that hyperalgesia is achieved by a variety of parenteral routes of injection. Histological evaluation of rat spinal cord and dorsal root ganglia revealed no neurodegenerative changes 24 h after kainic acid. Together these data suggest that a persistent hyperalgesia results from the transient activation of AMPA/KA receptors that are located outside the spinal cord, perhaps on the distal projections of primary afferent fibers.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Hindlimb; Hot Temperature; Hyperalgesia; Injections, Intraperitoneal; Kainic Acid; Male; Mice; Mice, Inbred Strains; Physical Stimulation; Piperazines; Rats; Rats, Sprague-Dawley; Touch

The GABA(A) receptor antagonist bicuculline methiodide (BMI, 10 microM) transformed the evoked synaptic responses, recorded intracellularly from the CA3 area of neonatal (postnatal days 3-7, P3-P7), juvenile (P8-P20) and adult hippocampal slices, into long-lasting paroxysmal depolarizations (PDs), with repetitive action potentials (APs). In the same preparation, GABA(A)-mediated fast-IPSPs were depolarizing at resting membrane potential (RMP), with a reversal potential shifting to a hyperpolarizing direction with age (n=15, P6-P17). BMI provoked also spontaneous PDs in juvenile (20/30) and adult (7/10) but not in neonatal (0/12) neurons. PDs were depressed by either the NMDA receptor antagonist CPP (10 microM) or the non-NMDA antagonist CNQX (10 microM), but were blocked only by the combination of the two (n=6), indicating that activation of either NMDA or non-NMDA receptors can independently sustain PDs in immature hippocampus. In conclusion, these findings show that endogenous GABA tonically inhibits CA3 synaptic responses in neonatal life despite the depolarizing nature of GABA(A)-mediated potentials. Moreover, they suggest that during the 1st postnatal week, disinhibition alone is not sufficient to provoke spontaneous epileptiform discharges in CA3 hippocampal area.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Aging; Animals; Animals, Newborn; Bicuculline; Epilepsy; Excitatory Amino Acid Antagonists; GABA Antagonists; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid; In Vitro Techniques; N-Methylaspartate; Piperazines; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate

Field potential and intracellular recordings were made in slices of human neocortical tissue obtained during surgery for the treatment of seizures associated with focal cortical dysplasia. Ictal-like epileptiform discharges, along with isolated field potentials, were induced by bath application of 4-aminopyridine (50-100 microM). Some of the isolated field potentials were associated with fast transients representing population spikes. Field potential profile analysis indicated that both types of synchronous activity had maximal negative values at 1,400 to 1,600 microm from the pia. The intracellular counterpart of the ictal-like discharge was a prolonged membrane depolarization capped by repetitive action potential burst firing. By contrast, the isolated field potentials were mirrored by long-lasting depolarizations with minimal action potential firing; only when population spikes occurred, the isolated field potentials were associated with epileptiform action potential bursting. Ictal-like discharges were abolished by either N-methyl-D-aspartate or non-N-methyl-D-aspartate receptor antagonists. In contrast, the isolated field potentials continued to occur synchronously during excitatory transmission blockade (although they lacked fast transients) but were abolished by the gamma-aminobutyric acid(A) receptor antagonist bicuculline methiodide (n = 2 slices). Our study demonstrates that focal cortical dysplasia tissue maintained in vitro has an intrinsic ability to generate ictal-like epileptiform events when challenged with 4-aminopyridine. These discharges depend on excitatory amino acid receptor-mediated mechanisms. Our results also show the presence in focal cortical dysplasia tissue of glutamatergic-independent synchronous potentials that are mainly contributed by gamma-aminobutyric acid(A) receptor-mediated conductances.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Adolescent; Adult; Anticonvulsants; Cerebral Cortex; Child; Electroencephalography; Epilepsies, Partial; Epilepsy, Frontal Lobe; Epilepsy, Temporal Lobe; Evoked Potentials; Female; Humans; In Vitro Techniques; Magnetic Resonance Imaging; Male; Membrane Potentials; Piperazines

Expression of GAP-43 in the cerebellum and selected regions of the brain has been shown to be developmentally regulated. Localization of GAP-43 mRNA within granule cells of the immature and mature rat cerebellum has been demonstrated by in situ hybridization. Higher levels are detected in the neonate compared to the adult. To determine if the cerebellar neurotransmitters, GABA (gamma-amino-butyric acid) and glutamate are involved in the modulation of GAP-43 expression, cultured cerebellar granule cells were exposed to these transmitters. Cultures were treated with glutamate, GABA, or the agonists/antagonists to their receptors in serum-free media for 5-7 days. Analysis of the levels of GAP-43 mRNA by in situ hybridization indicated that a 7-day exposure to GABA (25 and 50 microM) significantly lowered levels of granule cell GAP-43 mRNA. Specific agonists to the GABAA (muscimol) and GABAB (baclofen) receptors produced a decrease similar to that observed for GABA. Results from these studies also indicated that exposure to non-NMDA (CNQX) and NMDA (CPP, MK-801) glutamate receptor antagonists, and a metabotropic receptor glutamate agonist (ACPD), decreased the level of GAP-43 mRNA. The involvement of GABA and glutamate in the modulation of GAP-43 expression was corroborated by Northern hybridization. These studies revealed that a 5-day exposure to GABA decreased the cellular content of GAP-43 mRNA by 21% whereas exposure to glutamate resulted in a 37% increase. Findings from the studies reported here, using an in vitro cerebellar granule cell model, suggest that levels of GAP-43 mRNA, in vivo, are modulated by input from both excitatory glutamatergic mossy fibers and inhibitory GABAergic Golgi interneurons. Thus, modulation of GAP-43 mRNA by these neurotransmitters may influence granule cell maturation during development in the neonate and neuroplasticity in the adult, possibly at the parallel fiber-Purkinje cell synapse.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Baclofen; Blotting, Northern; Cells, Cultured; Cerebellum; Cycloleucine; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; GABA Agonists; gamma-Aminobutyric Acid; GAP-43 Protein; Gene Expression Regulation, Developmental; Glial Fibrillary Acidic Protein; Glutamic Acid; Immunohistochemistry; In Situ Hybridization; Microtubule-Associated Proteins; Muscimol; N-Methylaspartate; Neurons; Neuroprotective Agents; Piperazines; Rats; Rats, Sprague-Dawley; RNA, Messenger

1. Interictal and ictal epileptiform discharges induced by 4-aminopyridine (4AP, 50 microM) were studied in the rat lateral entorhinal cortex with field potential and intracellular recordings in an in vitro slice preparation. Both types of discharge disappeared in layer II, but continued to occur in layers IV-VI after a knife cut separation was made at approximately 600 micro(m) from the pia (n = 4 slices). 2. Interictal depolarizations recorded in layer IV-VI cells (amplitude, 29.4 +/- 8.6 mV; duration, 386 +/- 177.4 ms, means +/- s.d.; n = 17) were capped by action potential bursts, while smaller interictal depolarizations in layer II cells (amplitude, 11.7 +/- 5.8 mV; duration, 192.6 +/- 47.9 ms; n = 10) were associated with single action potentials and were terminated by a hyperpolarization. Ictal discharges were initiated by an interictal discharge; they were characterized by a depolarization of 31.5 +/- 6.2 mV (n = 12) in layer IV-VI and 11.6 +/- 3.5 mV (n = 7) in layer II neurones. 3. Slow, presumptive Ca2+-mediated spikes occurred in layer II (n = 4) and IV-VI (n = 6) cells loaded with the Na+ channel blocker QX-314 (50 mM). These events were synchronized with population spikes during interictal and ictal discharges, and were abolished by Ni2+ (1 mM, n = 4 cells) along with the 4AP-induced synchronous activity. 4. The N-methyl-D-aspartate (NMDA) receptor antagonist 3, 3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonate (CPP, 10 microM) abolished ictal discharges and reduced interictal depolarizations in layer IV-VI neurones (n = 4). The non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) abolished both interictal and ictal activity (n = 4 cells). 5. These findings provide evidence for a role played by NMDA-mediated mechanisms in the generation of epileptiform discharges in the entorhinal cortex. Lack of an NMDA-mediated component along with presence of inhibition in layer II neurones results in attenuation of epileptiform activity at this site. Moreover Ca2+-mediated spikes may contribute to the appearance of epileptiform discharges in this model.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Calcium; Electrophysiology; Entorhinal Cortex; Epilepsy; Excitatory Amino Acid Antagonists; Male; Neurons; Organ Culture Techniques; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Intracellular recordings from CA3 pyramidal cells of rat hippocampus in a slice preparation revealed the occurrence of interictal epileptiform discharges and synchronous GABA-mediated potentials during application of 4-aminopyridine (4AP, 50 micrometer). The synchronous GABA-mediated potential consisted of a sequence of early hyperpolarization, long-lasting depolarization (LLD), and late hyperpolarization. Action potentials of variable amplitude occurred at the peak of the early hyperpolarization and during the LLD rising phase (48 of 64 cells); they were not prevented by membrane hyperpolarization and displayed inflections that were reminiscent of the initial segment-somatodendritic (IS-SD) fractionation. Interictal discharges were blocked by excitatory amino acid receptor antagonists, while both GABA-mediated potentials and action potentials of variable amplitude continued to occur (n = 10). The latter events were still recorded in the presence of the GABAB receptor antagonist CGP-35348 (0.5-1 mm, n = 4), but were abolished by the GABAA receptor antagonist bicuculline methiodide (BMI, 10 micrometer, n = 5). Localized application of BMI (20 micrometer, n = 6) or tetrodotoxin (TTX, 5 micrometer, n = 3) to the CA1 stratum radiatum blocked the variable amplitude action potentials; these effects were not seen when BMI (n = 4) or TTX (n = 4) were applied to the CA3 stratum radiatum, although both procedures made LLDs disappear. Our findings indicate that action potentials of variable amplitude recorded from CA3 pyramidal cells in the 4AP model are generated at or near the terminal region of the Schaffer collaterals and that they represent TTX-sensitive ectopic events. These action potentials are generated at this site by a BMI-sensitive (and thus GABAA-mediated) mechanism. We propose that the ectopic action potentials reflect an increased excitability of axon terminals that is presumably caused by [K+]o elevations associated with the 4AP-induced synchronous GABA-mediated potential.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Bicuculline; Excitatory Amino Acid Antagonists; GABA Antagonists; GABA-A Receptor Antagonists; GABA-B Receptor Antagonists; gamma-Aminobutyric Acid; Hippocampus; In Vitro Techniques; Male; Patch-Clamp Techniques; Piperazines; Rats; Rats, Sprague-Dawley; Tetrodotoxin; Time Factors

The role of glutamate receptors in regulating programmed neuronal death and deafferentation-induced neuronal death in the brainstem auditory nuclei was studied by in ovo drug administration to chick embryos. The nucleus laminaris (NL) undergoes programmed developmental cell death of 19% between embryonic day 9 (E9) and E17. The AMPA/kainate receptor antagonist CNQX, when administered at doses of 200-300 microg/d from E8 to E15, prevented programmed neuronal death in NL through at least posthatching day 8, without producing anatomical or behavioral abnormalities. 3-((RS)-2-Carboxypiperazin-4-yl)-propyl-1-phos-phonic acid, an antagonist of NMDA receptors, had no effect on normal cell death in the NL. CNQX, given from E8 to E15 or only from E8 to E10, also blocked the 33% neuronal loss in the nucleus magnocellularis (NM) that follows surgical destruction of the otocyst on E3, a procedure that deafferents NM neurons by preventing formation of the cochlear nerve. Treatment either with CNQX or the more highly selective NBQX from E8 to E10, before the onset of synaptic transmission in NM and NL, was also effective in preventing normal neuronal death in NL. Analysis of the effects of CNQX or NBQX on spontaneous embryonic motility at E10 showed that the doses effective in preventing neuronal death suppressed motility for <8 hr. We conclude that periodic blockade of AMPA/kainate receptors can protect CNS neurons against subsequent programmed cell death or deafferentation-induced death.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Auditory Pathways; Brain Stem; Cell Death; Cell Survival; Chick Embryo; Excitatory Amino Acid Antagonists; Kinetics; Neurons; Piperazines; Quinoxalines; Receptors, AMPA; Receptors, Kainic Acid; Time Factors

Ethanol, usually studied in relation to intoxication, is also capable of producing general anesthesia. The most common standard of anesthetic potency is the concentration which produces immobility in response to a noxious stimulus. This concentration will be referred to as the anesthetic concentration. Immobilization is a spinal effect. Ethanol effects were studied in spinal cord from 2-7-day-old rats at concentrations which included the anesthetic concentration in both adult rats (97 mM) and 6-7-day-old rats (235 mM). At neonatal but not adult anesthetic concentrations, ethanol depressed monosynaptic reflex amplitude (mediated by glutamate AMPA receptors + compound action potential). At both neonatal and adult anesthetic concentrations ethanol reversibly depressed the population excitatory postsynaptic potential (pEPSP) (glutamate AMPA and NMDA receptors), the slow ventral root potential (NMDA + metabotropic receptors), and the dorsal root potential (GABA(A) receptors, via glutamate-excited interneurons). Effects were greater on NMDA receptor-mediated components than on AMPA-receptor-mediated components of the pEPSP and greater on NMDA than on metabotropic receptor-mediated components of the slow ventral root potential. The profile of ethanol effects on spinal cord resembles that of inhalation general anesthetics. The results show that both AMPA and NMDA receptor-mediated transmission are sensitive to ethanol and that enhancement of GABAergic neurotransmission is overridden by depression of excitation to the interneurons. They provide no obvious explanation for ethanol's lower general anesthetic potency in the neonate.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Anesthetics, General; Animals; Animals, Newborn; Ethanol; Evoked Potentials; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; In Vitro Techniques; Piperazines; Rats; Receptors, AMPA; Receptors, Kainic Acid; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Reflex, Monosynaptic; Spinal Cord; Spinal Nerve Roots; Synaptic Transmission

This study was aimed at identifying the neuronal pathways that mediate the eating-induced increase in the release of dopamine in the nucleus accumbens of the rat brain. For that purpose, a microdialysis probe was implanted in the ventral tegmental area and a second probe was placed in the ipsilateral nucleus accumbens. Receptor-specific compounds acting on GABA(A) (40 microM muscimol; 50 microM bicuculline), GABA(B) (50 microM baclofen), acetylcholine (50 microM carbachol), NMDA [30 microM (+/-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP)], and non-NMDA [300 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)] receptors were infused into the ventral tegmental area by retrograde dialysis, whereas extracellular dopamine was recorded in the ipsilateral nucleus accumbens. Intrategmental infusion of muscimol or baclofen decreased extracellular dopamine in the ipsilateral nucleus accumbens; CPP and CNQX were without effect, and bicuculline and carbachol increased dopamine release. During infusion of the various compounds, food-deprived rats were allowed to eat for 10 min. The infusions of muscimol, bicuculline, baclofen, carbachol, and CNQX did not prevent the eating-induced increase in extracellular dopamine in the nucleus accumbens. However, during intrategmental infusion of CPP, the eating-induced increase in extracellular dopamine in the nucleus accumbens was suppressed. These results indicate that a glutamatergic projection to the ventral tegmental area mediates, via an NMDA receptor, the eating-induced increase in dopamine release from mesolimbic dopamine neurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Baclofen; Bicuculline; Carbachol; Dopamine; Eating; Excitatory Amino Acid Antagonists; GABA Agonists; GABA Antagonists; Male; Microdialysis; Muscimol; Nucleus Accumbens; Parasympathomimetics; Piperazines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Tegmentum Mesencephali

1. Field potential recordings and measurements of the extracellular concentration of free K+ ([K+]o) and Ca2+ ([Ca2+]o) were made during application of 4-aminopyridine (4-AP, 50 microM) in hippocampal slices that were obtained from 11- to 32-day-old rats. 2. Spontaneous field potentials recorded under this experimental condition in the CA3 stratum radiatum of slices from rats < 23 days old consisted of interictal (duration, 0.2-1.4 s; intervals of occurrence, 0.9-3.4 s) and ictal epileptiform discharges (duration, 5-46 s; intervals of occurrence, 22-259 s) and negative-going potentials that often preceded the onset of ictal discharge. Ictal activity became rare in slices from rats > 25 days old. 3. The negative-going potential (which also corresponded to the ictal discharge onset) was associated with [K+]o increases to 9.4 +/- 3.6 mM (mean +/- S.D.) from 3.25 mM baseline (n = 11 slices). [K+]o remained elevated at 5-6 mM throughout the ictal event. Decreases in [Ca2+]o (from 1.8 mM baseline to 1.3 +/- 0.1 mM, n = 7) were observed during the ictal discharge. 4. Interictal and ictal discharges were abolished by the non-N-methyl-D-aspartate (NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2, 3-dione (CNQX, 10 microM). CNQX and the NMDA receptor antagonist 3-((+/-)-2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP) did not influence negative-going potentials or the associated [K+]o increases (peak values were 8.7 +/- 3.2 mM, n = 8), that were blocked, however, by bicuculline methiodide (BMI, 10 microM). 5. The mu-opioid receptor agonist (D-Ala2,N-Me-Phe4,Gly5-ol)-enkephalin (DAGO, 10 microM) which inhibits GABA release from interneurons, prevented the occurrence of both GABA-mediated synchronous potentials and subsequent ictal discharges (n = 6) as well as the [K+]o elevations. DAGO effects were antagonized by naloxone (10 microM; n = 4). 6. The GABA-mediated [K+]o elevations changed as a function of age. In hippocampal slices obtained from 11- to 17-day-old rats, peak values of 10.6 +/- 2.0 mM (n = 10) and half-width durations of 8.7 +/- 1.3 s (n = 7) were observed. In slices obtained from 25- to 32-day-old animals these parameters were 5.2 +/- 0.5 mM (n = 13) and 4.6 +/- 1.1 s (n = 4), respectively. 7. This study shows that, in the juvenile rat hippocampus, 4-AP induces a glutamatergic independent synchronous potential that is due to GABA released from inhibitory terminals and is associated with an increase in [K+]o. This [K+]o elevation undergoes

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Aging; Analgesics; Animals; Calcium; Electrophysiology; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Excitatory Amino Acid Antagonists; Extracellular Space; Hippocampus; Membrane Potentials; Patch-Clamp Techniques; Piperazines; Potassium; Rats; Receptors, Opioid, mu

The purpose of the present study was to determine whether blockade of excitatory amino acid receptors at the ventrolateral nucleus of the tractus solitarius would influence respiratory activity. This was done by microinjecting excitatory amino acid receptor antagonists into the ventrolateral nucleus of the tractus solitarius of alpha-chloralose-anesthetized animals while monitoring respiratory activity using a Fleisch pneumotachograph and arterial blood pressure and heart rate. Bilateral microinjection of the NMDA receptor antagonist, 3-[(R)-carboxypiperazin-4-yl]-propyl-1- phosphomic acid (CPP), 5.62 nmol per side, produced an increase in inspiratory duration (+4 +/- 1.6 s, n = 8) which progressed to an apneustic pattern of breathing. Similar results were obtained with CPP microinjected into the ventrolateral nucleus of the tractus solitarius of three vagotomized animals. Bilateral microinjection of a second NMDA receptor antagonist, 2-amino-7-phosphono-heptanoic acid (AP7), 562 nmol per side, produced qualitatively similar effects on respiration as seen with CPP. In contrast, blockade of non-NMDA receptors with 6-cyano-7-nitroquinoxaline-2,3-dione (CNXQ), 0.125 nmol per side, had very little effect on respiration. Activation of NMDA receptors at the ventrolateral nucleus of the tractus solitarius with bilateral microinjection of NMDA, 39 pmol, produced a large increase in expiratory duration (+11 +/- 3 s, n = 8), and apnea during the expiratory phase of the respiratory cycle in half of the animals studied. Similar results were obtained with D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazol-proprionate (AMPA). These results indicate that an endogenous excitatory amino acid released at the ventrolateral nucleus of the tractus solitarius and acting at the NMDA receptor, plays a significant role in respiratory timing.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Amino Acids; Animals; Apnea; Blood Pressure; Cats; Female; Heart Rate; Male; Microinjections; N-Methylaspartate; Piperazines; Pulmonary Ventilation; Receptors, N-Methyl-D-Aspartate; Respiration; Solitary Nucleus; Vagotomy

Intracellular recordings were made from neurons in the motor cortex of an anaesthetized cat, together with iontophoretic application of excitatory amino acid receptor agonists and antagonists, in order to evaluate the role of such receptors in excitatory postsynaptic potentials evoked from stimulation of afferent and recurrent pathways in vivo. Excitatory postsynaptic potentials which were evoked by stimulation of the ventrolateral thalamus were found to be largely insensitive to antagonism by N-methyl-D-aspartate receptor antagonists, although they were susceptible to blockade by the non-N-methyl-D-aspartate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione. Increasing the ventrolateral thalamus stimulation frequency from 0.5 or 1 to 5 Hz caused an increase of evoked excitatory postsynaptic potential amplitudes and number of action potentials. These augmented excitatory postsynaptic potentials remained insensitive to application of N-methyl-D-aspartate antagonists. In contrast, recurrent excitatory postsynaptic potentials evoked by stimulation of the pyramidal tract were found to be sensitive to N-methyl-D-aspartate receptor antagonists and/or non-N-methyl-D-aspartate receptor antagonists in some neurons. These results demonstrate the involvement of both N-methyl-D-aspartate- and non-N-methyl-D-aspartate receptors in synaptic responses of cat motor cortex neurons in vivo, and that the synaptic pharmacology of the thalamic input may differ from that of the local recurrent pathways.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Cats; Electric Stimulation; Electrophysiology; Evoked Potentials; Female; Male; Motor Cortex; Piperazines; Pyramidal Tracts; Receptors, AMPA; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Thalamus

The behavioural and convulsant effects of imipenem (Imi), a carbapenem derivative, were studied after intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures. The anticonvulsant effects of some excitatory amino acid antagonists and muscimol (Msc), a GABAA agonist, against seizures induced by i.p. or i.c.v. administration of Imi were also evaluated. The present study demonstrated that the order of anticonvulsant activity in our epileptic model, after i.p. administration, was (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)-cyclohepten-5,10-imine maleate (MK-801) > (+/-)(E)-2-amino-4-methyl-5-phosphono-3-pentenoate ethyl ester (CGP 39551) > 3-((+/-)-2-carboxypiperazin-4-yl)propenyl-1-phosphonic acid (CPPene) > 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CCP) > 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)-quinoxaline (NBQX). Ifenprodil, a compound acting on the polyamine site of NMDA receptor complex was unable to protect against seizures induced by Imi, suggesting that the poliamine site did not exert a principal role in the genesis of seizures induced by Imi. In addition, the order of anticonvulsant potency in our epileptic model, after i.c.v. administration, was CPPene > MK-801 > Msc > (-)-2-amino-7-phosphonic acid (AP7) > gamma-D-glutamylaminomethylsulphonate (gamma-D-GAMS) > NBQX > kynurenic acid (KYNA) > 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX). The relationship between the different site of action and the anticonvulsant activity of these derivatives was discussed. Although the main mechanism of Imi induced seizures cannot be easily determined, potential interactions with the receptors of the excitatory amino acid neurotransmitters exists. In fact, antagonists of excitatory amino acids are able to increase the threshold for the seizures or to prevent the seizures induced by Imi. In addition, Imi acts on the central nervous system by inhibition of GABA neurotransmission and Msc, a selective GABAA agonist, was able to protect against seizures induced by Imi.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Anticonvulsants; Dizocilpine Maleate; Excitatory Amino Acids; Glutamine; Imipenem; Kynurenic Acid; Mice; Mice, Inbred DBA; Muscimol; Piperazines; Piperidines; Quinoxalines; Seizures

Implantable sustained-release polymers offer an alternative to osmotic minipumps for the local delivery of drugs to specific brain areas. Here we describe the production of Elvax polymers containing a range of glutamate receptor antagonists and the quantitative characterization of their release properties. Sections of Elvax (200 or 400 microns), prepared by a dimethyl sulphoxide-based method, containing the NMDA antagonist MK-801 or the non-NMDA antagonist CNQX exhibited similar release profiles: an initial 2-week burst followed by a slow decline in release rate over the next 6 weeks. Differences in slice preparation method and thickness or drug concentration and solubility all led to alterations in the level of drug release, but not the overall exponential nature of the release curve. Elvax sections prepared by an aqueous method containing the NMDA antagonists CPP or APV displayed more constant but much lower levels of release than those from the dimethyl sulphoxide-based method. The in vitro release characteristics were compared with in vivo release of MK-801 and the close correspondence observed indicates that the in vitro release data is an accurate predictor of the drug release behaviour of implanted Elvax slices.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Dizocilpine Maleate; Drug Carriers; Drug Implants; Excitatory Amino Acid Antagonists; Ferrets; Molecular Weight; N-Methylaspartate; Piperazines; Polyvinyls; Receptors, Glutamate

The purposes of our study were to determine the type of respiratory changes that would occur when either an excitatory amino acid receptor agonist or an uptake inhibitor was administered into the caudal subretrofacial area. This was done by microinjecting either L-glutamate or L-pyrrolidine-2,4-dicarboxylate (L-trans-2,4-PDC) into the caudal subretrofacial area while monitoring tidal volume, respiratory rate, mean arterial blood pressure and heart rate. Bilateral microinjection of 2.5 nmol of L-glutamate into the caudal subretrofacial area produced apnea in eight of eight animals tested, and the duration of apnea was 27 +/- 2 s. To determine the type of L-glutamate receptor responsible for mediating the apneic response, antagonists of the N-methyl-D-aspartate (NMDA) and non-NMDA receptor, namely, 3-[(RS)-carboxypiperazin-4-yl]-propyl-phosphonic acid (CPP), and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), respectively, were tested. Neither antagonist in doses that blocked NMDA (in the case of CPP) and amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) (in the case of CNQX) blocked apnea elicited by L-glutamate. In addition, kynurenic acid, an antagonist of NMDA and non-NMDA ionotropic receptors, failed to block the effect of L-glutamate. Microinjection of the metabotropic receptor agonist drug, trans-L-1-amino-1,3-cyclopentone-dicarboxylic acid (L-trans-ACPD), into the caudal subretrofacial area failed to have any effect on respiratory activity. Because of the inability to block the effect of L-glutamate in the caudal subretrofacial area, and the lack of effect of L-trans-ACPD, the data suggest that the apneic response produced by L-glutamate is mediated by an as yet undefined receptor. Microinjection of the L-glutamate uptake inhibitor, L-trans-2,4-PDC, was found to produce apnea. Using the dose of 0.5 nmol of L-trans-2,4-PDC, we examined the type of excitatory amino acid receptor that mediated the response. Neither pretreatment with the NMDA receptor antagonist, CPP, nor the non-NMDA receptor antagonist, CNQX, affected L-trans-2,4-PDC-induced apnea. However, combined use of these two antagonists prevented L-trans-2,4-PDC-induced apnea. These data suggest that the effect of synaptically released exitatory amino acid at the caudal subretrofacial area on breathing is apnea, and that this effect is mediated by simultaneous activation of both NMDA and non-NMDA ionotropic receptors.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Apnea; Blood Pressure; Cats; Cycloleucine; Dicarboxylic Acids; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Heart Rate; Kynurenic Acid; Male; Neurotoxins; Neurotransmitter Uptake Inhibitors; Piperazines; Pyrrolidines; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Respiration; Respiratory Function Tests; Tidal Volume; Trigeminal Caudal Nucleus

Slow inhibition was investigated by stimulating inhibitory neurons at the border of stratum radiatum and lacunosum-moleculare with focal microapplications of glutamate, while recording resultant slow inhibitory postsynaptic potentials in CA1 pyramidal neurons in rat hippocampal slices. The slow inhibitory postsynaptic potentials evoked had an average peak amplitude of -2.2 mV, measured at -60 mV. Their peak conductance was 2.5 nS. These events were characterized as slow GABAB inhibitory postsynaptic potentials because they reversed at -90 mV, and were blocked by CGP 35348 (500 microM). Exposure to magnesium-free solutions augmented glutamate-evoked slow inhibitory postsynaptic potentials. Mean peak amplitude and conductance were -3.1 mV and 4.0 nS. Exposure to the N-methyl-D-aspartate antagonist MK-801 (20 microM) allowed separation of the glutamate-triggered slow inhibitory postsynaptic potential into components induced by non-N-methyl-D-aspartate and N-methyl-D-aspartate receptor activation. The N-methyl-D-aspartate component dominated, even under control conditions, and could account for up to 60% of the control slow inhibitory postsynaptic potential. Thus, the activation and recruitment of GABAB-mediated inhibition depend on both non-N-methyl-D-aspartate and N-methyl-D-aspartate-mediated excitation of inhibitory interneurons. Under physiological conditions slow inhibition may act as an important synaptic filtering mechanism, but when N-methyl-D-aspartate-mediated excitation increases, slow inhibition is further recruited, providing an important means to offset excessive excitation.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; GABA Antagonists; GABA-B Receptor Antagonists; Glutamic Acid; Hippocampus; In Vitro Techniques; Interneurons; N-Methylaspartate; Organophosphorus Compounds; Patch-Clamp Techniques; Piperazines; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Receptors, GABA-B; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission

Pilocarpine injection into rodents leads to the development of chronic limbic seizures that follow an initial status epilepticus and a seizure-free interval. It has been proposed that a decreased efficacy of the mechanisms that buffer the extracellular concentration of K+ ([K+]o) leads to an increase in seizure susceptibility. Therefore, we analyzed the changes in [K+]o associated with the synchronous activity induced by 4-aminopyridine (4AP) in hippocampal slices obtained from control and pilocarpine-treated rats. At all recording sites (i.e. stratum radiatum of the CA1 and CA3 subfields, and hilus of the dentate gyrus), the amplitude of GABA-mediated synchronous field potentials induced by 4AP, as well as the associated [K+]o increases, were significantly reduced in slices obtained from the pilocarpine-treated rats. In the control group, the field-potential amplitudes reached 1 mV (i.e. 1.7 +/- 0.3 mV in CA1, 0.93 +/- 0.2 mV in CA3, and 1.03 +/- 0.12 mV in the hilus; mean +/- SEM), while the accompanying rises in [K+]o exceeded 4 mM (i.e. 4.17 +/- 0.15 mM in CA1, 4.04 +/- 0.12 mM in CA3, 4.04 +/- 0.11 mM in the hilus) from a baseline of 3.25 mM. The corresponding values in slices from the pilocarpine-treated group were rarely greater than 0.4 mV (i.e. 0.3 +/- 0.09 mV in CA1, 0.27 +/- 0.03 mV in CA3 and 0.38 +/- 0.06 mV in the hilus), and larger than 3.6 mM (i.e. 3.63 +/- 0.04 mM in CA1, 3.64 +/- 0.03 mM in CA3 and 3.60 +/- 0.04 mM in the hilus) from a similar baseline value. With pilocarpine, the rate of occurrence of the GABA-mediated potential significantly decreased from 0.035 to 0.016 s-1. Since the rises in [K+]o decreased rather than increased and their overall duration was unchanged (possibly reflecting cell loss), we conclude that a modification of [K+]o buffering capacity is unlikely to account for the appearance of in vivo seizures in the pilocarpine model of epilepsy.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Evoked Potentials; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Extracellular Space; Hippocampus; In Vitro Techniques; Male; Muscarinic Agonists; Pilocarpine; Piperazines; Potassium; Rats; Seizures

Whole-cell recording techniques were used to record isolated slow inhibitory postsynaptic currents in CA1 pyramidal neurons from rat hippocampal slices. Application of 6-cyano-7-nitroquinoxaline-2,3-dione and 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid eliminated excitatory synaptic transmission, resulting in a 38% reduction in slow inhibitory postsynaptic current magnitude. Subsequent addition of the GABAA antagonist picrotoxin caused a further decrease in slow inhibitory postsynaptic current amplitude. The remaining, isolated slow inhibitory postsynaptic current was blocked by the GABAB antagonist 2-hydroxysaclofen and when cesium was substituted for intracellular potassium. The kinetics of isolated slow inhibitory postsynaptic currents were characterized by single exponential, fourth power activation, and double exponential inactivation. These slow inhibitory postsynaptic currents had a reversal potential of -85.7 +/- 1.6 mV, and a slope conductance of 935 +/- 277 pS. Single slow inhibitory postsynaptic currents carried a total charge flux of 13.4 +/- 7.6 pC. Repetitive stimulation up to 1 Hz progressively reduced steady-state slow inhibitory postsynaptic current amplitude. This attenuation was characterized by a decrease in slope conductance, but slow inhibitory postsynaptic current reversal potential remained unchanged, as did slow inhibitory postsynaptic current kinetics. These results indicate that, under physiological conditions, both ionotropic glutamate- and GABAA-mediated transmission contribute to slow inhibitory postsynaptic current recruitment. Given this finding, activity-dependent decreases in GABAA transmission could contribute to slow inhibitory postsynaptic current depression, though not exclusively, since isolated slow inhibitory postsynaptic currents also demonstrated this property. The use-dependent depression of isolated slow inhibitory postsynaptic currents may be a consequence of a reduction in transmitter release.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Electrophysiology; GABA-B Receptor Antagonists; Hippocampus; In Vitro Techniques; Ion Channels; Kinetics; Membrane Potentials; Patch-Clamp Techniques; Picrotoxin; Piperazines; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Receptors, GABA-B; Receptors, N-Methyl-D-Aspartate; Synapses

The caudal ventrolateral medulla (CVLM) has been shown to participate in the reflex airway dilation evoked by stimulation of thin fiber afferents innervating the hindlimb of anesthetized dogs. Nevertheless, the pharmacological mechanism in the CVLM by which hindlimb afferents evoke this reflex airway dilation is not known. Therefore, we examined the role played by excitatory amino acid receptors in the CVLM in the reflex airway dilation arising from the hindlimb. Using chloralose-anesthetized dogs, we found that bilateral microinjections into the CVLM of either (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (25 mM, 50 nl) or (+/-)-2-amino-5-phosphonovaleric acid (50 mM, 50 nl), both of which block N-methyl-D-aspartate (NMDA) receptors, reversibly attenuated the decrease in total lung resistance that was evoked by either electrical stimulation of C-fibers in the sciatic nerve or by static contraction of both gastrocnemius muscles. In contrast, bilateral microinjection into the CVLM of 6-cyano-7-nitroquinoxaline-2,3-dione (39 microM, 50 nl), which blocks non-NMDA receptors, augmented the reflex decrease in total lung resistance that was evoked by either sciatic nerve stimulation or contraction of the gastrocnemius muscles. Bilateral microinjections of xanthurenic acid (100 mM, 50 nl) into the CVLM had no effect on the decrease in total lung resistance that was evoked by sciatic nerve stimulation. We conclude that NMDA, but not non-NMDA, receptors in the CVLM play an important role in the reflex arc that dilates the airways when hindlimb afferents are stimulated by either muscular contraction or electrical stimulation.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Airway Resistance; Animals; Dogs; Electric Stimulation; Hindlimb; Lung; Medulla Oblongata; Microinjections; Muscle Contraction; Muscle, Skeletal; Neurons, Afferent; Piperazines; Receptors, N-Methyl-D-Aspartate; Reflex; Sciatic Nerve

Spontaneous synchronous field potentials of negative polarity (duration = 200-700 ms, inter-event interval = 9.1 +/- 2.9 s; n = 27 slices) were recorded, during application of 4-aminopyridine (50 microM), from the superficial/middle layers of slices of human neocortex obtained in the course of neurosurgery for the relief of intractable seizures. The negative-going field potential corresponded to an intracellular long-lasting (duration = 200-1600 ms) depolarization that could be preceded by preceded by an excitatory postsynaptic potential-hyperpolarizing inhibitory postsynaptic potential sequence and followed by a long-lasting hyperpolarization. This synchronous activity continued to occur following blockade of excitatory synaptic transmission by excitatory amino acid receptor antagonists, but was greatly reduced and eventually disappeared during application of the GABAA receptor antagonist bicuculline methiodide. Simultaneous extracellular recordings from three sites in the slice located along an axis parallel to the pia showed that successive synchronous field potentials could originate from any of the three areas. They invaded the other two sites in c. 35.5% of the cases, while propagation to another site only or no propagation at all was observed, respectively, in 44.4% and 20% of instances. The velocity of lateral propagation of the synchronous field potential was 7.9 +/- 2.5 mm/s (range = 4.5-11.8 mm/s, n = 6). The modalities of origin and propagation remained the same after blockade of excitatory amino acid receptors. Under these conditions, however, there was a higher incidence of non-propagation and the velocity was significantly lower than in control (5.6 +/- 1.9 mm/s; range = 2.8-7.7 mm/s, n = 6). These data indicate that, in the human neocortex, 4-aminopyridine can reveal a synchronous field potential that correlates with an intracellular long-lasting depolarization and is mainly due to the activation of postsynaptic GABAA receptors. The action of excitatory amino acid receptors is not necessary for the generation and propagation of these GABA-mediated potentials. We propose that this potential represents a novel mechanism for synchronization and spread of neuronal activity, including seizure-like discharges in the human neocortex.

Topics: 2-Amino-5-phosphonovalerate; 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Cerebral Cortex; Female; gamma-Aminobutyric Acid; Humans; Male; Piperazines; Tetrodotoxin

The contribution of NMDA and non-NMDA receptors to visual synaptic transmission in the superficial layers of the superior colliculus of the cat has been studied using extracellular recording and iontophoretic techniques. Neuronal responses to natural visual stimulation and the ejection of NMDA and AMPA were observed in the absence and presence of the antagonists CNQX, CPP and AP5. CNQX routinely reduced the responses to visual stimulation at ejection currents which selectively blocked the responses to AMPA but not those to NMDA. Agonist selective ejection currents of CPP and AP5 also reduced visual responses of most SC neurons, but there was a substantial majority whose visual responses were resistant to these antagonists. Neurons with CPP/AP5 resistant visual responses were more commonly found 750-1000 microns from the dorsal surface of the SC. The data indicate that, while non-NMDA receptors are heavily involved in visual synaptic transmission in the superficial SC, the involvement of NMDA receptors varies with recording depth.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cats; Electrodes; Electrophysiology; Female; Iontophoresis; Ocular Physiological Phenomena; Photic Stimulation; Piperazines; Quinoxalines; Receptors, Amino Acid; Receptors, N-Methyl-D-Aspartate; Superior Colliculi; Synapses; Synaptic Transmission; Vision, Ocular

Considerable evidence suggests that both substance P and glutamate play a role in the spinal transmission of the exercise pressor reflex. We tested two hypotheses. First, after a lumbosacral intrathecal injection of a glutamatergic receptor antagonist, the reflex cardiovascular and ventilatory responses to static contraction are attenuated. Second, after a lumbosacral intrathecal injection of a substance P receptor antagonist and a glutamatergic receptor antagonist, the reflex cardiovascular and ventilatory responses to static contraction are abolished. We found that 1) the reflex cardiovascular responses to static contraction were unaffected (P > 0.05) after the intrathecal injection of the N-methyl-D-aspartate (NMDA) receptor antagonists, dl-2-amino-5-phosphonopentanoate (+/- AP-5) or 3-[(+-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid (+/- CPP); 2) the reflex pressor response to static muscular contraction was attenuated by > 50% after the intrathecal injection of the non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX); and 3) the reflex pressor response to static contraction was almost abolished after the intrathecal injection of the substance P receptor antagonist, CP-96,345, and CNQX. Our results suggest that substance P and glutamate are two neurotransmitters involved in the spinal transmission of the exercise pressor reflex and that substance P and glutamate exert their effects via neurokinin-1 (NK-1) and non-NMDA receptors, respectively.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Biphenyl Compounds; Blood Pressure; Cats; Heart Rate; Hypnotics and Sedatives; Injections, Spinal; Muscle Contraction; Neurokinin-1 Receptor Antagonists; Piperazines; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Time Factors

Recent studies have reported that microinjection of kynurenic acid (KYN 12.5 nmol), the nonselective Excitatory Amino acid (EAA) antagonist, into the rostral ventrolateral medulla of the cat decreases arterial blood pressure (BP) and inferior cardiac sympathetic nerve discharge. The purpose of our study was to confirm this finding and determine the subtypes of EAA receptor(s) responsible for mediating this effect. This was done by microinjecting various EAA antagonists bilaterally into the SRFN of chloralose-anesthetized animals while monitoring BP and HR. KYN (12.5 nmol; N = 5) produced a decrease in mean BP (31 +/- 9 mmHg, P < .05) with no significant change in HR. To determine the subtype of EAA receptor responsible for eliciting tonic sympathetic outflow from the SRFN, specific antagonists of N-methyl-D-aspartate (NMDA) and non-NMDA EAA receptors were tested. The NMDA receptor antagonist 3-(RS)-Carboxypiperazin-4-yl)-proyl- 1-phosphonic acid (CPP-2.25 nmol; N = 3) microinjected into the SRFN produced a small but significant decrease in BP (-13 +/- 1 mmHg; P < .05). This effect of CPP was significantly less than that seen with KYN. Two antagonists of the non-NMDA subtype of EAA receptor, 6-cyano-7-nitroquinoxaline-2,3-dione (0.05 nmol; N = 4) and gamma-D-glutamylaminomethyl sulphonic acid (2.5 nmol; N = 4), were microinjected into the SRFN. Both of these drugs produced decreases in BP (-29 +/- 4 and -23 +/- 3 mmHg, respectively; P < 0.05) similar to that observed with KYN. No significant changes in HR were noted with CPP, 6 cyano-7-nitroquinoxaline-2,3-dione or gamma-G-glutamylamino-methylsulfonate. These data indicate that a non-NMDA EAA receptor plays the major role in control of cardiovascular function by the SRFN.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Blood Pressure; Cardiovascular Physiological Phenomena; Cats; Female; Glutamine; Kynurenic Acid; Male; Medulla Oblongata; Microinjections; Neurons; Piperazines; Quinoxalines; Receptors, Amino Acid; Receptors, N-Methyl-D-Aspartate

1. We have examined the effects of iontophoretic application of antagonists to excitatory amino acid (EAA) receptors, as well as glycine and gamma-aminobutyric acid (GABA), on rhythmically active (RA) brain stem neurons during cortically induced masticatory activity (RMA) in the anesthetized guinea pig. Ten of these neurons were antidromically activated at latencies of 0.3-0.9 ms by stimulation of the trigeminal motor nucleus (MoV). 2. RA neurons were divided into closer and opener type according to the phase of activation during RMA. Iontophoretic application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a specific non-N-methyl-D-aspartate (NMDA) receptor antagonist, suppressed discharge of both closer and opener type RA neurons during RMA. In contrast, iontophoretic application of 3-((1)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), a specific NMDA receptor antagonist, was not effective in suppressing discharge of most opener type RA neurons but did reduce activity of closer type RA neurons. 3. Spike discharge of most RA neurons was time locked to each cortical stimulus during RMA. Some of the RA neurons were activated at a short latency to short pulse train stimulation of the cortex in the absence of RMA. In most cases CNQX reduced such time-locked responses during RMA and greatly reduced discharge evoked by short pulse stimulation of the cortex in all cases. In contrast, CPP was not as effective in suppressing either the time-locked responses during RMA or the discharge evoked by short pulse train stimulation of the cortex. 4. D,L-Homocysteic acid (HCA) application produced low level maintained discharge in RA neurons before RMA induction. When RMA was evoked in combination with HCA, rhythmical burst discharges with distinct interburst periods during the opening phase of RMA were observed in most closer type RA neurons. In contrast, during RMA in combination with HCA application, opener type RA neurons showed burst discharges that were modulated during the RMA cycle but lacked distinct interburst periods during the closer phase of the cycle. 5. During application of strychnine (STR), a glycine antagonist, discharge of closer type RA neurons increased in the opener phase of RMA during continuous HCA application. In contrast, bicuculline methiodide (BIC), a GABA antagonist, did not increase unit discharge of closer type RA neurons in the opener phase of RMA. 6. It is concluded that closer type RA neurons receive, alternatively, EAA-mediated

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Brain Mapping; Brain Stem; Cerebral Cortex; Electric Stimulation; Excitatory Amino Acid Antagonists; GABA Antagonists; Guinea Pigs; Homocysteine; Interneurons; Mastication; Membrane Potentials; Neural Inhibition; Neural Pathways; Piperazines; Reaction Time; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Strychnine; Synaptic Transmission; Trigeminal Nerve; Trigeminal Nuclei

Anatomic and physiologic studies in the rat have shown projections from the hippocampal formation (HF) and mediodorsal (MD) thalamic nucleus to the medial prefrontal cortex (mPFC). The authors used multi-barrel iontophoresis to: confirm the neurotransmitter used in the projection from HF to mPFC; investigate the role of GABAergic inhibition in the regulation of this projection; and examine the functional convergence of projections from HF and MD onto single mPFC neurons. During HF stimulation, nine cells (6%) showed excitation followed by prolonged inhibition, 39 cells (26%) showed prolonged inhibition alone and 100 cells (68%) showed no clear response. In a further 12 cells that showed no predrug excitation to HF stimulation (representing 16% of the cells in this category), iontophoresis of the GABAA antagonist bicuculline methiodide (BMI) revealed excitatory responses. A total of six mPFC cells (38% of the cells showing excitatory responses to HF stimulation) showed convergent excitation to HF and MD thalamic (or adjacent paratenial nucleus) stimulation. Five out of eight (63%) of the predrug or BMI-revealed excitatory responses of mPFC neurons to HF stimulation were selectively decreased after AMPA antagonist iontophoresis (either CNQX or DNQX). These data confirm that the HF projection to prefrontal cortex is, at least in part, glutamatergic; suggest that the responses of mPFC neurons to activity in this HF pathway are regulated by GABAergic inhibition; and indicate that projections from HF and MD converge onto single mPFC neurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Baclofen; Bicuculline; Brain Mapping; Electric Stimulation; Electrophysiology; GABA-A Receptor Antagonists; GABA-B Receptor Antagonists; gamma-Aminobutyric Acid; Glutamic Acid; Limbic System; Male; Neurons; Organophosphorus Compounds; Piperazines; Prefrontal Cortex; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Thalamus

1. The effects of glutamate receptor agonists and antagonists on bipolar cells and ganglion cells were studied with the use of intracellular and extracellular recording in the superfused, isolated, flat-mounted tiger salamander retina. The goal of the experiments was to correlate glutamate receptor subtypes with their localization at specific synaptic sites in the tiger salamander retina. The drugs tested were the kainate/alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), the N-methyl-D-aspartate (NMDA) receptor antagonist 3-(C+/-)-2-carboxy-piperazin-4-yl)-propyl-1-phosphonic acid (CPP) and L-2-amino-4-phosphonobutyrate (L-AP4). 2. The light responses of hyperpolarizing bipolar cells were suppressed by 20 microM CNQX, whereas L-AP4 had no effect on their light responses. In contrast, 20 microM CNQX had no effect on depolarizing bipolar cells, whereas L-AP4 abolished the light responses of these cells. 3. The light offset responses of OFF and ON-OFF ganglion cells were completely blocked by concentrations of CNQX as low as 5 microM. The light onset responses of ON-OFF ganglion cells were blocked when the concentration of CNQX was raised to 20 microM. In addition, 30 microM CPP partially blocked the light onset responses of ON-OFF ganglion cells but had a lesser effect on the light offset responses. 4. Twenty micromolars of CNQX blocked a transient component, and 20 microM CPP blocked a sustained component of the light response of sustained-ON ganglion cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Ambystoma; Aminobutyrates; Animals; Glutamates; Ibotenic Acid; In Vitro Techniques; Kainic Acid; Photic Stimulation; Piperazines; Quinoxalines; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Retina; Retinal Ganglion Cells; Synapses

Extracellular field potential recordings were used to study the epileptiform activity evoked by tetraethylammonium (TEA) in the CA3 subfield of hippocampal slices obtained from young (12-18 day-old) and adult (> 60-day-old) rats. During TEA application (5-10 mM), young slices generated both ictal-like (duration: up to 28 s, rate of occurrence 1-3 x 10(-2) s-1) and interictal-like (duration: 1.5-2 s; rate of occurrence: 1-3 x 10(-1) s-1) activity. In adult slices only interictal-like activity was induced by TEA (3-10 mM). Depending on the concentrations of TEA, these events lasted 80-600 ms and occurred at 5-60 x 10(-2) s-1. Both the N-methyl-D-aspartate (NMDA) receptor antagonist 3-3(2-carboxypiperazine-4-yl)propyl-1-phosphonate (5-10 microM; CPP) and the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (5-10 microM; CNQX) were necessary to suppress ictal-likeand interictal-like discharges in young slices. By contrast, interictal-like activity in adult slices was reduced and eventually blocked by CNQX (0.5-3 microM) alone. Furthermore the pattern of epileptiform discharges seen in young slices was modified by CPP (i.e. decrease in the rate of occurrence of ictal events and reduction in the duration of interictal discharges), while the activity recorded in adult slices was resistant to this NMDA antagonist. Bicuculline methiodide (5 microM; BMI) enhanced the duration of epileptiform activities in both young and adult slices. Our data demonstrate that the epileptiform discharges induced by TEA in the CA3 subfield of the rat hippocampus display age-dependent patterns of activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Aging; Animals; Bicuculline; Dose-Response Relationship, Drug; Epilepsy; Evoked Potentials; GABA-A Receptor Antagonists; Hippocampus; In Vitro Techniques; Male; Piperazines; Pyramidal Tracts; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Tetraethylammonium; Tetraethylammonium Compounds

The propagation of sustained potential shifts associated with spreading depression (SD) was studied by microelectrodes placed in diverse layers at different locations in hippocampus of anesthetized rats. SD was induced by raising interstitial potassium concentration ([K+]0) focally in the CA1 region of the dorsal hippocampus either by microdialysis or by microinjection. Recurrent waves of SD propagated from the dialysis site throughout the hippocampus. Potential shifts (delta V0) associated with SD usually began earlier and were always of larger amplitude and longer duration in stratum (st.) radiatum (layer of apical dendrites) than in st. pyramidale (layer of pyramidal cell somata). The velocity of propagation in the two layers differed and varied independently one from the other. When SD was provoked by orthodromic train stimuli, the apparent direction of propagation in st. pyramidale was opposite that in st. radiatum. Microinjection of high K+ solution was more likely to provoke SD when placed in the st. radiatum, 50-100 microns ventral to st. pyramidale, than in other cytoarchitectonic layers. In about half the trials after 30 to 90 min of high K+ dialysis, a prolonged depressed state developed during which the potential in st. radiatum shifted at irregular intervals between near-rest level and a strongly negative level, while delta V0 shifts in st. pyramidale were smaller and more irregular in amplitude. This state is termed prolonged unstable SD". When the NMDA receptor antagonist CPP was dialyzed together with high K+, the onset of SD was postponed and delta V0 waves propagated in st. pyramidale without corresponding waves in st. radiatum; less frequently the other way around.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Dendrites; Dialysis; Electrophysiology; Female; Hippocampus; In Vitro Techniques; Microinjections; Neurons; Piperazines; Potassium; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Spontaneous spreading depression episodes were studied in CA1 and CA3 areas of immature hippocampal slices (two to 30 days postnatally) during 4-aminopyridine (50 microM) perfusion. Spreading depression occurred in the CA3 area of 34% of all slices tested (two to 30 days postnatally). The duration and frequency of the spreading depression field potentials changed with development. In the CA3 area, their duration decreased from 169 +/- 22 s (n = 17, postnatal days to to 10) to 55 +/- 7 s (n = 10, postnatal days 21-30), their rate of occurrence increased from four episodes per hour (0.0011 +/- 0.0001 Hz, n = 11, postnatal days two to 10) to 6.5 episodes per hour (0.0018 +/- 0.0003 Hz, n = 8, postnatal days 21-30), while their amplitude remained stable (10-30 mV). Spreading depression d.c. potential shift originated closer to CA1 than CA3. Furthermore, spreading depression field potentials had greater magnitude (amplitude and duration) in CA1. Spreading depressions were reversibly blocked by the N-methyl-D-aspartate receptor antagonist 3,3-(2-carboxy-piperazine-4-yl)-propyl-1-phosphonate (CPP, 1-5 microM, n = 15), but were not affected by 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX, 2-5 microns, n = 11), which is a non-N-methyl-D-aspartate receptor antagonist. The GABAA receptor antagonist bicuculline methiodide (3-10 microM) initially favored and then blocked spreading depression in 79% of the slices tested (n = 16). In addition, bicuculline impaired spreading depression propagation from CA1 to CA3. 4-Aminopyridine also induced the appearance of other types of spontaneous activity, such as ictal and interictal-like epileptiform discharges. The effects of 3,3-(2-carboxy-piperazine-4-yl)-propyl-1-phosphonate, 6-cyano-7-nitro-quinoxaline-2,3-dione and bicuculline on epileptiform activity were opposite to those on spreading depression. Our findings demonstrate that spreading depression can occur as early as two days postnatally and that the characteristics of this phenomenon change with maturation. These results also indicate that 4-aminopyridine-induced spreading depression episodes and epileptiform activity are mediated by the activation of different types of excitatory amino acid receptors. Finally, spreading depression is influenced by blockade of the GABAA receptor.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Cortical Spreading Depression; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid; Hippocampus; Piperazines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate

We have studied in situ the excitability state of the axon-soma membrane of CA1 pyramidal cells in the rat during synaptic activation of N-methyl-D-aspartate (NMDA) receptors. Repetitive activation (3-5 Hz) of Schaffer collaterals provoked a NMDA receptor-mediated component in the field excitatory postsynaptic potential (fEPSP) within 15 s. The generation of this component follows a characteristic self-limiting cycle, vanishing after 6-10 s. When alvear shocks were paired to the orthodromic volleys, the antidromic population spike (PS) was completely abolished only if the NMDA receptor-mediated fEPSP had occurred. This blockade of antidromic invasion lasted for 120-150 ms after each orthodromic shock. A reduction in the safety factor for axon-soma transmission is presumed during NMDA receptor synaptic activation.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Axons; Electric Stimulation; Evoked Potentials; Hippocampus; Piperazines; Pyramidal Tracts; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Stereotaxic Techniques; Synapses; Time Factors

Extracellular field recordings were performed in guinea-pig and rat neocortical slice preparations maintained in vitro. Bath application of the convulsant drug 4-aminopyridine (4-AP, 100 microM) induced spontaneous epileptiform potentials in 80% of the guinea-pig neocortical slices and only in 6% of the neocortical slices from rat. In both species spontaneous epileptiform activity consisted of a 4-16 s long ictal-like discharge that recurred with a frequency range of 0.01-0.02 Hz. In rat neocortical slices stimulus-induced responses resembled the spontaneous occurring epileptiform events. Ictal-like discharges in guinea-pig neocortical slices were blocked by the N-methyl-D-aspartate (NMDA) receptor antagonist 3-((+/-)-2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (5 microM), while those in the rat disappeared during perfusion with the non-NMDA excitatory amino acid receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (1-3 microM). These results indicate that the neocortex of guinea-pig has a higher propensity to generate 4-AP-induced spontaneous epileptiform activity than that of rat. Furthermore the epileptiform activity in these two species requires a different involvement of excitatory amino acid receptors.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Anticonvulsants; Cerebral Cortex; Electric Stimulation; Electrophysiology; Epilepsy; Guinea Pigs; In Vitro Techniques; Piperazines; Quinoxalines; Rats; Receptors, N-Methyl-D-Aspartate

Spontaneous episodes of spreading depression (SD) were observed in the CA3 subfield of immature or young (2-30 days postnatally) hippocampal slices perfused with medium containing 4-aminopyridine (4-AP, 50 microM). SD appeared in 34% of the hippocampal slices examined and was more frequently observed in slices obtained from 11 to 20-day-old animals. SD studied with extracellular field potential recordings consisted of large amplitude (18.7 +/- 1.1 mV, mean +/- S.E.M.) negative DC shifts that lasted 30-250 s. Unlike the epileptiform activity that was concomitantly seen during 4-AP application, SD was blocked by the NMDA receptor antagonist 3-((RS)-2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP, 2-10 microM). In contrast, 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX, 5 microM), a non-NMDA-type receptor antagonist, blocked the epileptiform activity but only increased the interval between SD episodes. These results demonstrate that immature hippocampal tissue is susceptible to SD episodes, when perfused with 4-AP-containing medium, and that the occurrence of these episodes presumably depends on the activation of the NMDA receptor. In addition these findings indicate that SD shows a sensitivity to excitatory amino acid receptor antagonists that differs from that of the epileptiform activity recorded simultaneously.

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Aging; Animals; Animals, Newborn; Anticonvulsants; Dendrites; Epilepsy; Evoked Potentials; Hippocampus; In Vitro Techniques; Membrane Potentials; Models, Biological; Piperazines; Pyramidal Tracts; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate

A single unilateral injection of carrageenan (4.5-6.0 mg in 0.15-0.20 ml saline) into the rat hindpaw induced behavioral hyperalgesia as evidenced by a significant reduction in hindpaw withdrawal latency to a noxious thermal stimulus. The involvement of N-methyl-D-aspartate (NMDA) receptors in this model of hyperalgesia was examined by intrathecal administration of the selective excitatory amino acid (EAA) receptor antagonists: (+/-)-2-amino-5-phosphonopentanoic acid (AP-5), (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), ketamine hydrochloride (ketamine), 7-chlorokynurenic acid (7-Cl kynurenic acid), and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The effects of dizocilpine maleate (MK-801) were studied under the same conditions and published previously (Ren et al., 1992) and the data are presented for comparison. While the withdrawal latencies of the non-injected paws and of the paws of naive rats were not significantly affected by application of the EAA receptor antagonists at doses tested, the paw withdrawal latencies of the carrageenan-injected paws were elevated dose dependently. The rank order of potency of these agents to reduce hyperalgesia was: MK-801 greater than or equal to AP-5 greater than or equal to CPP = 7-Cl kynurenic acid = ketamine much greater than CNQX greater than 0. In contrast, intrathecal injection of the opioid receptor agonists, [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAMGO, mu-selective) and [D-Pen2,D-Pen5] enkephalin (DPDPE, delta-selective), produced antinociception in both injected and non-injected paws. DAMGO was much more potent, while DPDPE was less potent, than MK-801.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Analgesics; Analysis of Variance; Animals; Behavior, Animal; Carrageenan; Dizocilpine Maleate; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalins; Hyperalgesia; Inflammation; Injections, Spinal; Ketamine; Kynurenic Acid; Male; Piperazines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Valine

The effect of excitatory amino acid receptor antagonists, (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5, 10-imine hydrogen maleate ((+)-MK-801), (+/-)-3-(2-carboxy-piperazin-4-yl)-propyl-1-phosphonic acid (CPP), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and (+/-)-2-amino-4-phosphonobutanoic acid (AP-4), on penile erection and yawning induced by subcutaneous apomorphine (80 micrograms/kg), intracerebroventricular (i.c.v.) oxytocin (30 ng) and adrenocorticotropin (ACTH)-(1-24) (10 micrograms) was studied in male rats. Intraperitoneal (0.1-0.4 mg/kg) and i.c.v. (10-50 micrograms) (+)-MK-801 prevented dose dependently the penile erection and yawning induced by the three drugs. The (+)-MK-801 effect coincided with the appearance of head weaving, body rolling, hyperlocomotion and ataxia. Haloperidol (0.5 mg/kg i.p.) antagonized the prevention by (+)-MK-801 of oxytocin responses. Penile erection but not yawning was also prevented by high, but not low doses of CPP and CNQX, which impaired motor performance, AP-4 was ineffective at all doses tested. The above compounds were ineffective when injected into the paraventricular nucleus of the hypothalamus, the brain area where apomorphine and oxytocin act to induce penile erection and yawning. The results suggest that excitatory amino acid transmission is not involved in the expression of penile erection and yawning induced by the above compounds.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Adrenocorticotropic Hormone; Aminobutyrates; Animals; Apomorphine; Dizocilpine Maleate; Dose-Response Relationship, Drug; Injections, Intraperitoneal; Injections, Intraventricular; Injections, Subcutaneous; Male; Oxytocin; Penile Erection; Piperazines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Amino Acid; Yawning

1. We have examined the actions and pharmacology of two putative optic nerve transmitters, N-acetylaspartylglutamate (NAAG) and L-homocysteic acid (L-HCA), in the feline dorsal lateral geniculate nucleus (dLGN). We compared the responses obtained to iontophoretic application of these substances with those elicited by visual stimulation and application of specific N-methyl-D-aspartate (NMDA) and non-NMDA receptor agonists. The relative effects of the selective NMDA antagonist 3-[(+/-)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid (CPP) and the selective non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were tested on these responses. 2. There was a pronounced contrast between the influence of iontophoretically applied NAAG and L-HCA on dLGN cells. Iontophoretic application of NAAG [ejection current range 75-200 nA (mean 125 nA)] evoked either no effect (17/37), or very weak and sluggish excitatory (16/37) or inhibitory (4/37) effects. Conversely, L-HCA application [current range 25-136 nA (mean 67 nA)] elicited brisk and powerful excitatory responses (32/32) that were comparable with those produced by visual stimulation and iontophoresis of NMDA, kainate, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). 3. Responses to L-HCA were selectively antagonized by application of the NMDA receptor antagonist CPP but were generally much less affected by the non-NMDA receptor antagonist CNQX. The weak and inconsistent responses to NAAG were not compatible with an evaluation of antagonist effects. 4. CPP application at dose levels selective for NMDA with respect to kainate and AMPA did not exert equal effects on L-HCA and NMDA. Whereas the mean responses to L-HCA were reduced to 32% of control for Y cells and 21% for X cells, those to NMDA were 11 and 11%, respectively. However, the level of reduction of the visual response for X and Y cells was very similar to that of L-HCA, visual responses being reduced to 35 and 22% of control for Y and X cells. 5. CNQX application reduced the visual response level of Y cells to 64% of control and that of X cells to 65%. The mean level for the L-HCA response of Y cells was 106% of control; the mean for X cells, 79%, was substantially below control. The responses to kainate and AMPA were reduced to a much greater extent. 6. The data suggest that it is unlikely that NAAG is the optic nerve transmitter.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cats; Dipeptides; Female; Geniculate Bodies; Homocysteine; Immunohistochemistry; Iontophoresis; Neurons; Neurotransmitter Agents; Photic Stimulation; Piperazines; Quinoxalines

Conventional intracellular recordings were made from regular-spiking cells located in layers II-IV to examine the involvement of excitatory amino acid receptors in synaptic transmission in epileptogenic human neocortical slices maintained in vitro. Extracellular stimuli that were below the threshold for generating action potentials evoked an excitatory postsynaptic potential (EPSP) with short latency to onset (0.8-4 ms). When suprathreshold stimuli were delivered, 95% of the neurons fired a single action potential. In 5% of the population, however, an all-or-none bursting discharge was observed. The EPSP and the bursting discharge were tested with the N-methyl-D-aspartate (NMDA) antagonist 3-((+/-)-2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP, 5 microM) or the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 4 microM). In the presence of CNQX the peak amplitude of the EPSP was reduced by 85% and the bursting discharge was abolished completely. By contrast, CPP reduced the peak amplitude of the EPSP by 52%, attenuated the late phase of the bursting discharge and increased its threshold. These results indicate that excitatory amino acids function as excitatory transmitters in the human brain. While the involvement of non-NMDA receptors in the EPSP is in line with data from normal neocortical slices of other mammals, the participation of NMDA-mediated conductances to the EPSP appears peculiar to the epileptogenic human neocortex. This evidence, together with the contribution of NMDA and non-NMDA receptors to the all-or-none bursting discharge suggests that excitatory amino acid-mediated transmission might be modified in the epileptogenic human neocortex.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Adult; Cerebral Cortex; Epilepsy; Evoked Potentials; Humans; Membrane Potentials; Organ Culture Techniques; Piperazines; Psychosurgery; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Cells, Cultured; Cerebellum; Dizocilpine Maleate; Ibotenic Acid; Kainic Acid; N-Methylaspartate; Neurons; Piperazines; Quinoxalines; Quisqualic Acid; Rats; Receptors, N-Methyl-D-Aspartate; Taurine

1. Postsynaptic currents originating from activation of the two major excitatory inputs to Purkinje cells were studied in thin slices of rat cerebellum, using the tight-seal whole-cell recording technique. Two types of excitatory postsynaptic currents were analysed: those evoked by stimulation of the granule cell-parallel fibre system (PF-EPSC) and those elicited by stimulation of the climbing fibres (CF-EPSC). 2. Both types of postsynaptic currents had a linear current-voltage relation, reversing at membrane potentials close to 0 mV. Their time course of activation was independent of the membrane potential. 3. For both types of postsynaptic currents, the time course of decay was well described by a single exponential function, with a time constant which increased as the membrane potential was made more positive. 4. Postsynaptic currents arising from stimulation of the climbing fibre generally had a slightly faster time course of onset and decay than those associated with stimulation of the granule cell-parallel fibre system. The average values of the 10-90% rise time were 1.8 +/- 0.4 ms (means +/- S.D., n = 7) for PF-EPSCs and 0.8 +/- 0.3 ms (n = 9) for CF-EPSCs. Time constants of decay, at a holding potential of -60 mV, had values of 8.3 +/- 1.6 ms (n = 7) and 6.4 +/- 1.1 ms (n = 9) for PF-EPSCs and CF-EPSCs respectively. 5. CF-EPSCs and PF-EPSCs had the characteristics described above in slices derived from animals aged 9-22 days old and 9-15 days old, respectively. The PF-EPSCs in animals older than 15 days had very slow time courses and positive apparent reversal potentials, suggesting that they originated from distal locations, not under accurate voltage control. 6. In order to assess the quality of the voltage clamp, responses to hyperpolarizing pulses from -70 mV were analysed. The capacitive currents could be fitted by the sum of two exponentials, and were interpreted with an equivalent electrical circuit comprising two main compartments (soma and proximal dendrites on one hand, distal dendrites on the other). Analysis of synaptic currents in terms of this model suggested that the recorded time course of decay was approximately correct. 7. CF-EPSCs as well as PF-EPSCs were insensitive to the NMDA receptor antagonist 3-3(2-carboxypiperazine-4-yl)propyl-1-phosphonate (CPP), but were blocked in a dose-dependent reversible manner by the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX).(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Bicuculline; Electric Stimulation; Glutamates; Kainic Acid; Membrane Potentials; Piperazines; Purkinje Cells; Quinoxalines; Quisqualic Acid; Rats; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter

beta-p-Chlorophenylglutamate (Chlorpheg), a specific L-homocysteate (L-HC) uptake blocker, was tested on the L-HC- and L-glutamate-induced currents and on the excitatory postsynaptic potentials (EPSPs) evoked in CA1 rat hippocampal neurons by Schaffer collaterals stimulation. In the presence of tetrodotoxin (TTX; 1 microM), Chlorpheg (0.5-2 mM) potentiated L-HC- but not L-glutamate-induced currents. In normal magnesium containing medium and at resting membrane potential, Chlorpheg (1.5-1 mM) increased the amplitude and duration of the EPSPs evoked by Schaffer collaterals stimulation. This effect was prevented by bath application of the N-methyl-D-aspartate (NMDA) receptor antagonist CPP (20 microM). Chlorpheg enhanced also the NMDA component of the EPSP, evoked in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM), bicuculline (20 microM) and glycine (100 microM). This effect was blocked by CPP (20 microM). It is concluded that L-HC is an endogenous NMDA agonist at the Schaffer collateral-CA1 synapse.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Evoked Potentials; Glutamates; Glycine; Hippocampus; Homocysteine; In Vitro Techniques; Male; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Synapses; Tetrodotoxin

In the present work the distribution of L-glutamate binding sites in the different layers of human cerebellum of normal individuals and of seven patients who died with olivopontocerebellar atrophy (OPCA) was examined with the technique of quantitative autoradiography. Specific L-[3H]glutamate binding was higher in the molecular than in the granule cell layer of normal cerebellar tissue. A significant decrease of L-[3H]glutamate specific binding was observed in the molecular layer of all OPCA tissues. In the granule cell layer L-[3H]glutamate binding was decreased only in two patients who suffered from late-onset sporadic OPCA and in one patient who suffered from a form of OPCA inherited in a dominant manner. Quisqualate-sensitive binding sites were the most abundant binding sites in the molecular layer of normal cerebella, whereas N-methyl-D-aspartic acid (NMDA)-sensitive binding sites were the most abundant type in the granule cell layer. A significant decrease of quisqualate-sensitive and an increase in NMDA-sensitive binding sites were observed in the molecular layer of OPCA cerebellar tissues. No significant changes were observed in the granule cell layer of these tissues.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Adolescent; Adult; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Cerebellum; Female; Glutamates; Glutamic Acid; Humans; Ibotenic Acid; Male; N-Methylaspartate; Olivopontocerebellar Atrophies; Piperazines; Quinoxalines; Quisqualic Acid; Receptors, AMPA; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter

Excitatory amino acid receptors are involved in synaptic transmission throughout the central nervous system. As the specific synaptic pharmacology of visually responsive superior colliculus (SC) neurones has not been evaluated, we have attempted to antagonize visual responses of these neurones with selective excitatory amino acid antagonists. The N-methyl-D-aspartate (NMDA) receptor antagonist 3-((+/-)-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), and the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were applied iontophoretically in the vicinity of single visually responsive SC neurones. Visually evoked responses were antagonized by non-NMDA receptor selective currents of CNQX in 13 of 14 cells studied. Of 18 cells studied with NMDA receptor selective currents of CPP, visual responses were antagonized in only two cases. This study demonstrates that excitatory amino acid receptors are involved in synaptic transmission of visual information to the rat superior colliculus, but that NMDA receptors may play a relatively minor role.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Ibotenic Acid; Iontophoresis; Kainic Acid; N-Methylaspartate; Neurons; Photic Stimulation; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, Amino Acid; Receptors, Cell Surface; Receptors, N-Methyl-D-Aspartate; Superior Colliculi; Synapses

The involvement of excitatory amino acid (EAA) receptors in mediation of the toxic effects of cocaine was studied in male ICR mice. Cocaine HCl (90 mg/kg, IP) induced seizures in 95% and death within 24 h in 68% (n = 135) of the animals. There was a significant correlation (r = .54) between the time to onset of convulsions and the time to death in mice which died within 30 min of injection (n = 84). Pretreatment with selected EAA receptor antagonists 15 min prior to cocaine differentially blocked cocaine toxicity. Selective N-methyl-D-aspartic acid (NMDA) receptor antagonists (MK-801, dextrorphan, CPP) decreased both the incidence of seizures and mortality. A nonselective EAA antagonist, kynurenic acid, decreased lethality in doses which did not reduce convulsions. A similar action was observed following pretreatment with the selective kainic acid/AMPA receptor antagonist, GDEE. Antagonists at EAA receptors can provide significant protection against cocaine-induced toxicity. Moreover, the data provide evidence for the involvement of both NMDA and non-NMDA receptor subtypes in aspects of cocaine toxicity.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Anticonvulsants; Cocaine; Death; Dextrorphan; Dizocilpine Maleate; Dose-Response Relationship, Drug; Glutamates; Kynurenic Acid; Male; Mice; Mice, Inbred ICR; Piperazines; Quinoxalines; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Seizures; Time Factors

Conventional intracellular recording techniques were used to investigate the N-methyl-D-aspartate (NMDA) and non-NMDA mediated synaptic mechanisms underlying the stimulus-induced paroxysmal depolarization shift (PDS) generated by cells in rat neocortical slices treated with bicuculline methiodide (BMI). The NMDA receptor antagonists CPP or MK-801 were ineffective in abolishing the PDS. However, both drugs were able to attenuate the late phase of the PDS and delay its time of onset. In contrast, the non-NMDA receptor blocker CNQX demonstrated potent anticonvulsant property by reducing the PDS into a depolarizing potential that was graded in nature. This CNQX-resistant depolarizing potential was readily blocked by CPP. Voltage-response analysis of the PDS indicated that the entire response (including its NMDA-mediated phase) displayed conventional voltage characteristics reminiscent of an excitatory postsynaptic potential that is mediated by non-NMDA receptors. We conclude that the activation of non-NMDA receptors is necessary and sufficient to induce epileptiform activity in the neocortex when the GABAergic inhibitory mechanism is compromised. The NMDA receptors contribute to the process of PDS amplification by prolonging the duration and reducing the latency of each epileptiform discharge. However, the participation of NMDA receptors is not essential for BMI-induced epileptogenesis, and their partial involvement in the PDS is dependent upon the integrity of the non-NMDA mediated input. The lack of NMDA-like voltage dependency observed in the PDS's late phase might reflect an uneven distribution of NMDA receptors along the cell and/or an association of this excitatory amino acid receptor subtype in the polysynaptic pathways within the neocortex.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Bicuculline; Cerebral Cortex; Dizocilpine Maleate; Electric Stimulation; Epilepsy; In Vitro Techniques; Male; Membrane Potentials; N-Methylaspartate; Neurons; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, Amino Acid; Receptors, Cell Surface; Receptors, N-Methyl-D-Aspartate

The purpose of the present study was to identify sites(s) in the ventrolateral medulla where excitatory amino acids are involved in respiratory control. For this purpose, the respiratory effects produced by bilateral microinjection of excitatory amino acid antagonist drugs were examined while tidal volume (Vt), respiratory rate (f), arterial blood pressure and heart rate were monitored in chloralose-anesthetized cats. Microinjection of kynurenic acid (12.5 nmol) into a site approximately 3 mm rostral to obex, 4 mm lateral to midline and 1.5 mm below the ventral surface produced a decrease in Vt (-20 +/- 2 ml), an increase in f (+20 +/- 3 breaths/min) and a decrease in respiratory minute volume (-108 +/- 19 ml/min) (n = 8). These changes progressed to apnea in each animal tested. No significant changes in blood pressure or heart rate were observed. To determine the excitatory amino acid receptor subtype(s) involved, antagonists of n-methyl-D-aspartate (NMDA) (3-[(RS)-carboxypiperazin-4-yl]-propyl-1-phosphoric acid (CPP] and non-NMDA [6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)] receptors were microinjected bilaterally into this site. In the case of CPP, three doses were studied (0.25 nmol, n = 4; 0.75 nmol, n = 3; 2.25 nmol, n = 2). All three doses produced similar decreases in Vt (-12 +/- 1, P less than .05; -10 +/- 1, P less than .05; and -16 +/- 5 ml, respectively) and increases in f (+14 +/- 2, P less than .05; +10 +/- 3, P less than .05; and +12 +/- 3 breaths/min, respectively). None of these animals exhibited apnea.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Cats; Female; Glycine; Kynurenic Acid; Male; Medulla Oblongata; Microinjections; Piperazines; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Respiration

1. We have examined the effects of iontophoresing specific antagonists to excitatory amino acid receptors on the visual responses of cells in lamina A or A1 of the cat's lateral geniculate nucleus (LGN). 2. Cells were classified as On- or Off-center, X or Y, and lagged or nonlagged. The effects of antagonists were studied while cells were stimulated with spots of the appropriate contrast covering the receptive-field center. 3. The N-methyl-D-aspartate (NMDA) receptor antagonists D-2-amino-5-phosphonovaleric acid (D-APV) and 3-(+/-)-2-carboxypiperazin-4-yl)- propyl-1-phosphonic acid (CPP), when iontophoresed at doses that specifically antagonized NMDA-induced responses but not kainate-induced responses, reduced the responses of all cell types in the LGN, including X and Y cells, lagged and nonlagged cells, and On- and Off-center cells. 4. The non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), when applied at doses that specifically antagonized kainate-induced responses but not NMDA-induced responses, also reduced the visual responses of each of the cell types in the LGN. 5. We analyzed quantitatively the effects of D-APV and CNQX on LGN cells. D-APV reduced the responses of lagged cells to a greater extent than the responses of nonlagged cells. CNQX reduced the responses of lagged and nonlagged cells to a similar extent. There was no difference in the effect of D-APV or of CNQX on X and Y cells or on On- and Off-center cells. 6. We analyzed the effects of the antagonists on separate components of responses, including an early component comprising the first 100 ms of response and a late component comprising the next 300 ms of response. D-APV reduced the late component of lagged cell responses to a greater extent than either the early component of the same cells or the early or late component of nonlagged cells. CNQX had nearly equivalent effects on both response components of all cell types. 7. These data indicate that NMDA and non-NMDA receptors make similar contributions to the responses of On- and Off-center and X and Y cells in the LGN. Lagged and nonlagged cells are not differentiated with respect to the contribution of non-NMDA receptors to their visual responses. The greater contribution of NMDA receptors to the responses of lagged cells is consistent with the large contribution made by these receptors to the late response components of lagged cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cats; Electric Stimulation; Evoked Potentials; Geniculate Bodies; Kainic Acid; N-Methylaspartate; Neurons; Piperazines; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Synaptic Transmission; Time Factors; Visual Perception

The efflux of tritium from rat striatal synaptosomes labelled with [3H]dopamine was utilized as an index of dopamine (DA) release for the purpose of characterizing the receptors underlying the effects of L-glutamate. N-Methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA), and kainate each induced DA release in the absence of Mg2+, through NMDA was much more efficacious and only the NMDA response was inhibited by Mg2+. The response to L-glutamate was potentiated in a concentration-dependent manner by glycine. Further, it was completely inhibited by the competitive NMDA antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid and by the NMDA channel blocker phencyclidine. Finally, the response to L-glutamate was unaffected by either tetrodotoxin or the kainate-AMPA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. These data demonstrate the presence of NMDA receptors on dopaminergic nerve terminals that mediate the ability of L-glutamate to release DA and suggest an additional mechanism by which information from the nigrostriatal and corticostriatal pathways may be integrated.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Corpus Striatum; Dopamine; Female; Glutamates; Glutamic Acid; Glycine; In Vitro Techniques; Magnesium; Nerve Endings; Phencyclidine; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Substantia Nigra; Synaptosomes; Tetrodotoxin

1. Neuropharmacological actions of several kainate derivatives (kainoids) were examined for electrophysiological effects in the isolated spinal cord and the dorsal root fibre of the newborn rat. 2. Some kainoids caused depolarization of the motoneurone much more effectively than kainic acid or domoic acid and others were weaker. The rank order of the depolarizing activities of the kainoids tested here is as follows: 4-(2-methoxyphenyl)-2-carboxy-3-pyrrolidineacetic acid (MFPA) greater than acromelic acid A greater than domoic acid greater than or equal to 4-(2-hydroxyphenyl)-2-carboxy-3-pyrrolidineacetic acid (HFPA) greater than or equal to acromelic acid B greater than kainic acid. 3. In the isolated dorsal root fibre, domoic acid caused the most significant depolarization. There were distinct differences with regard to the rank order of the depolarizing activity between the motoneurone and the dorsal root fibre. The rank order in the dorsal root fibre is domoic acid greater than acromelic acid B greater than 5-bromowillardiine greater than or equal to MFPA greater than acromelic acid A greater than HFPA greater than kainic acid. 4. Significant desensitization of kainate receptors was observed in the isolated dorsal root fibre during prolonged application of L-glutamate, kainate and its derivatives. Cross desensitization was also observed among these excitatory amino acids. Receptors desensitized by kainate did not respond to MFPA, HFPA and acromelic acids, suggesting that these kainate derivatives activated common kainate receptors in the dorsal root fibre.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Animals, Newborn; In Vitro Techniques; Kainic Acid; Motor Neurons; Neuromuscular Depolarizing Agents; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Structure-Activity Relationship

The functional interaction in the spinal cord between substance P and excitatory amino acid agonists was investigated. Behavioural responses were scored in mice after intrathecal administration of excitatory amino acid agonists and substance P, given separately or in combination. A strong potentiation of the effect was seen when substance P was coadministered with N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) or kainic acid (KA). The potentiation was blocked by the corresponding antagonists: the selective NMDA-receptor antagonist (+/-)-3- (2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and the substance P analog, [D-Arg1,D-Trp7,9,Leu11]-substance P (Spantide). These findings indicate a functional interaction between substance P and glutamate in the dorsal horn of the spinal cord, compatible with the hypothesis that corelease of substance P and glutamate from primary afferent neurons may enhance nociception.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Amino Acids; Analgesics; Animals; Behavior, Animal; Drug Synergism; Ibotenic Acid; Injections, Spinal; Kainic Acid; Male; Mice; Mice, Inbred Strains; N-Methylaspartate; Nociceptors; Piperazines; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Substance P

Excitatory amino acids, that interact with the N-methyl-D-aspartate (NMDA) receptor stimulate release of [3H]dopamine [3H]DA) from the striatum of the guinea pig and rat in a concentration-dependent manner. DA release was measured in the presence of domperidone and nomifensine to avoid complications associated with autoreceptor alteration of and reuptake of released DA. This release is inhibited by magnesium. Therefore, all experiments were performed in the absence of this ion. The competitive NMDA antagonists D-(-)2-amino-5-phosphonopentanoic acid and 3-[(+-)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid and the noncompetitive antagonists (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine and phencyclidine also inhibit NMDA-stimulated release. Glycine enhances NMDA-stimulated release and can release [3H]DA in the absence of added NMDA. Release stimulated by glycine alone is not affected by 3-[(+-)-2-carboxypiperazine-4-yl]-propyl-1-phosphonic acid. Conversely, if the glycine antagonist 3-amino-1-hydroxy-2-pyrrolidone or 6-cyano-7-nitroquinoxaline-2,3-dione is included, NMDA elicits less release of [3H]DA. This inhibition can be overcome by increasing the concentration of glycine. The kappa-selective opioid agonist trans-(+-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]-benzene-acetamide is also capable of inhibiting the NMDA-stimulated release of [3H]DA from guinea pig and rat striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Corpus Striatum; Dopamine; Glycine; Guinea Pigs; Ion Channels; Magnesium; Male; N-Methylaspartate; Piperazines; Pyrrolidines; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid

The responses of single thalamic neurones to noxious thermal stimulation were recorded in anaesthetized rats. The selective N-methyl-D-aspartate (NMDA) receptor antagonist, 3-((+-)-2-carboxypiperazin-4-yl)propyl-l-phosphonate (CPP), antagonised nociceptive responses when ejected iontophoretically with currents which produced selective antagonism at NMDA receptors. In contrast, the non-NMDA excitatory amino acid receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNOX) had little or no effect on nociceptive responses, although it was able to reduce responses to non-nociceptive mechanoreceptor input. These results show that there is substantial NMDA receptor involvement in thalamic nociceptive responses, and that the contribution of CNQX-sensitive non-NMDA receptors to these responses is not extensive. Furthermore, it appears that nociceptive and non-nociceptive input to the thalamus have distinct synaptic pharmacologies.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Hot Temperature; Male; Nociceptors; Pain; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Thalamus

The N-methyl-D-aspartate receptor antagonist 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid and the non-N-methyl-D-aspartate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione have been iontophoretically applied to cells in the cat dorsal lateral geniculate nucleus and their effects on the visual response compared. The objective was to examine the possibility of both N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors being involved in the transfer of the retinal input to X and Y cells in the dorsal lateral geniculate nucleus. The results show that selective blockade of either N-methyl-D-aspartate receptors or non-N-methyl-D-aspartate receptors can block the visual response of both X and Y cells. Overall, the most potent reductions of visual responses across the population of cells studied were obtained with the N-methyl-D-aspartate receptor antagonist with X cells showing a slightly greater reduction on average (80%) than Y cells (66%). The relatively smaller overall reductions in visual responses obtained with the non-N-methyl-D-aspartate receptor blockade reflected the lower levels of blockade that were compatible with selectivity using iontophoretic applications of 6-cyano-7-nitroquinoxaline-2,3-dione. It is concluded that N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors are critically involved in the visual response of both "on" and "off" centre X and Y cells.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Cats; Female; Geniculate Bodies; Piperazines; Quinoxalines; Receptors, Amino Acid; Receptors, Cell Surface; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Retina; Retinal Ganglion Cells

Intrathecal administration of the preferential quisqualate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in anesthetized mice depressed Hoffmann (H)-reflexes, while flexor reflexes remained unaffected. The depressant effect of CNQX on H-reflexes was dose-dependent (range 0.1-10 nmol). The intrathecal administration of the selective N-methyl-d-aspartate (NMDA) antagonist 3-[(+-)-2-carboxypiperazin-4-yl]-propyl-1-phosphonate (CPP) reduced flexor reflexes (range 10-100 nmol) and had no effect on H-reflexes. These results suggest that H-reflexes in mice are mediated by spinal non-NMDA receptors, while flexor reflexes involve NMDA receptors.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; H-Reflex; Male; Mice; Piperazines; Quinoxalines; Receptors, Amino Acid; Receptors, Cell Surface; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Reflex, Monosynaptic; Spinal Cord

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Amino Acids, Dicarboxylic; Animals; Electric Stimulation; Ibotenic Acid; In Vitro Techniques; Inositol Phosphates; Kainic Acid; N-Methylaspartate; Piperazines; Quinoxalines; Quisqualic Acid; Rats; Rats, Inbred F344; Receptors, Glutamate; Receptors, Neurotransmitter; Synaptosomes

In primary cultures of rat cerebellar neurons, a brief stimulation of glutamate receptors results in coordinated activation of a programmed early gene response involving increases in the amount of c-fos, c-jun, jun-B, and zif/268 mRNAs. Each of these genes was induced to a different extent and showed a temporal pattern characterized by either a monophasic "early" response, occurring within 30 min of glutamate addition, or a biphasic response (c-jun), lasting for up to 6 to 8 hr after the initial stimulus. The early phase of the glutamate-induced gene expression was prevented by 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid, a highly selective isosteric antagonist of the N-methyl-D-aspartate (NMDA)-sensitive glutamate receptor (NMDA receptor). The second phase of the c-jun response was not blocked when the NMDA receptors were completely inhibited after the initial pulse of agonist or when the quisqualate-kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione was added, suggesting that a brief NMDA receptor stimulation triggers a cascade of events critical for the manifestation of the delayed c-jun expression. Furthermore, gel retardation assays demonstrated that NMDA receptor activation results in a prolonged increase in nuclear DNA-binding activity specific for the AP-1 transcriptional regulatory element. Protein immunoblot analysis showed that the composition of this nucleoprotein complex changes as a function of time, reflecting a cascade that involves an increased translation of Fos and several Fos-related proteins. The coordinated induction of several different transcription factors and the variations in transcriptional complex formation initiated by NMDA receptor stimulation may be a key mechanism in the orchestration of specific target gene expression that underlies various aspects of neuronal function, including plasticity responses.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cells, Cultured; Cerebellum; DNA-Binding Proteins; Gene Expression; Immunoblotting; N-Methylaspartate; Neurons; Phencyclidine; Piperazines; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-fos; Proto-Oncogene Proteins c-jun; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Transcription Factors; Transcription, Genetic

Rat cerebellar granule cells, when subjected to a glucose-free environment for 4 h, developed extensive degeneration of neuronal cell bodies and their associated neurite network over the following 24 h. This neuronal damage was quantitated with a colorimetric assay using the metabolic dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide. Hypoglycemic neuronal injury could be markedly reduced by the presence of both competitive (3-(+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid) and non-competitive (phencyclidine) N-methyl-D-aspartate receptor antagonists, but not by kainate/quisqualate preferring antagonists 6-cyano-7-nitroquinoxaline-2,3-dione and 6,7-dinitroquinoxaline-2,3-dione. Glucose deprivation neuronal injury was also reduced by adding glutamate-degrading enzymes to the incubation medium. Monosialoganglioside GM1, but not its asialo derivative (lacking sialic acid), was also effective in protecting against hypoglycemic neurodegeneration when included during the period of glucose deprivation. These results suggest that the neuronal injury to cerebellar granule cells resulting from glucose deprivation is mediated predominantly by activation of the N-methyl-D-aspartate type of excitatory amino acid receptor, perhaps through the action of endogenously released glutamate. Furthermore, the monosialoganglioside GM1, a member of a class of naturally occurring sialoglycosphingolipids, is able to attenuate this neuronal injury--as already observed for glutamate neurotoxicity and anoxic neuronal death in cerebellar granule cells. Gangliosides may thus prove to be of therapeutic utility in excitatory amino acid-associated neuropathologies.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cerebellum; G(M1) Ganglioside; Gangliosides; Hypoglycemia; Nerve Degeneration; Neurons; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, Amino Acid; Receptors, Cell Surface; Receptors, N-Methyl-D-Aspartate

The non N-methyl-D-aspartate (NMDA) receptor antagonists dinitroquinoxaline-2,3-dione (DNQX) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), both inhibit the visually driven response of sustained ganglion cells in the cat retina in vivo. In contrast to these findings, the potent NMDA receptor antagonist 3-[+/- )-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) has no effect. Thus, the endogenous excitatory amino acid released onto these cells on visual stimulation acts at non-NMDA receptors.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cats; In Vitro Techniques; Iontophoresis; Piperazines; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Retina; Retinal Ganglion Cells

Sensory synaptic responses of rat ventrobasal thalamus neurones were challenged with iontophoretic applications of the excitatory amino acid antagonists CNQX and CPP. CNQX, applied with currents which were selective for non-NMDA receptors, antagonised responses of VB neurones to both 10 ms and 2000 ms air jet stimulation of the peripheral receptive field. In contrast, CPP only antagonised the latter type of response. These results suggest a differential involvement of excitatory amino acid receptors in sensory synaptic transmission to the ventrobasal thalamus, with an initial synaptic component being mediated by non-NMDA receptors (including kainate receptors), and a further NMDA receptor-mediated component being manifested upon maintained sensory stimulation. The expression of this latter component appears to be largely dependent upon the integrity of the non-NMDA receptor-mediated component.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Amino Acids; Animals; Anticonvulsants; Male; Neurons, Afferent; Physical Stimulation; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, Amino Acid; Receptors, Cell Surface; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Thalamic Nuclei

The effects of excitatory amino acid antagonists on responses, evoked by myelinated primary afferent stimulation, in neurones of the spinal cord dorsal horn has been investigated in an isolated hemisected spinal cord preparation from the neonatal rat. The first evoked action potential of most responses was reversibly blocked by either 5 mM kynurenic acid (80%) or 10 microM CNQX (91%). The small latency variability and the ability of some of these responses to follow repetitive stimulation suggested that they were evoked monosynaptically. The selective NMDA receptor antagonist, CPP, blocked some later components of responses consisting of bursts of action potentials but not the first evoked action potential. The results support the suggestion that myelinated primary afferents release excitatory amino acids which act at kainate/quisqualate receptors.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Amino Acids; Animals; Animals, Newborn; Anterior Horn Cells; Electric Stimulation; Evoked Potentials; Kynurenic Acid; Myelin Sheath; Neurons, Afferent; Piperazines; Quinoxalines; Rats; Receptors, AMPA; Receptors, Kainic Acid; Receptors, Neurotransmitter; Spinal Cord

The N-methyl-D-aspartate (NMDA)-subtype of glutamate receptors has been well described as a result of the early appearance of NMDA antagonists, but no potent antagonist for the "non-NMDA" glutamate receptors has been available. Quinoxalinediones have now been found to be potent and competitive antagonists at non-NMDA glutamate receptors. These compounds will be useful in the determination of the structure-activity relations of quisqualate and kainate receptors and the role of such receptors in synaptic transmission in the mammalian brain.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Aspartic Acid; Binding, Competitive; Cell Membrane; Cerebral Cortex; Ibotenic Acid; Kainic Acid; Ketamine; N-Methylaspartate; Neurons; Piperazines; Quinoxalines; Rats; Receptors, AMPA; Receptors, Drug; Receptors, Glutamate; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Spinal Cord