6-cyano-7-nitroquinoxaline-2-3-dione and bicuculline-methiodide

Minocycline is a widely used glial activation inhibitor that could suppress pain-related behaviors in a number of different pain animal models, yet, its analgesic mechanisms are not fully understood. Hyperpolarization-activated cation channel-induced Ih current plays an important role in neuronal excitability and pathological pain. In this study, we investigated the possible effect of minocycline on Ih of substantia gelatinosa neuron in superficial spinal dorsal horn by using whole-cell patch-clamp recording. We found that extracellular minocycline rapidly decreases Ih amplitude in a reversible and concentration-dependent manner (IC50 = 41 μM). By contrast, intracellular minocycline had no effect. Minocycline-induced inhibition of Ih was not affected by Na(+) channel blocker tetrodotoxin, glutamate-receptor antagonists (CNQX and D-APV), GABAA receptor antagonist (bicuculine methiodide), or glycine receptor antagonist (strychnine). Minocycline also caused a negative shift in the activation curve of Ih, but did not alter the reversal potential. Moreover, minocycline slowed down the inter-spike depolarizing slope and produced a robust decrease in the rate of action potential firing. Together, these results illustrate a novel cellular mechanism underlying minocycline's analgesic effect by inhibiting Ih currents of spinal dorsal horn neurons.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Dose-Response Relationship, Drug; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; Lumbosacral Region; Male; Membrane Potentials; Membrane Transport Modulators; Minocycline; Patch-Clamp Techniques; Posterior Horn Cells; Rats, Sprague-Dawley; Strychnine; Substantia Gelatinosa; Tetrodotoxin; Tissue Culture Techniques

Unitary excitatory (EPSP) and inhibitory (IPSP) postsynaptic potentials (PSPs) were evoked between neurons in Rexed's laminae (L)II-V of spinal slices from young hamsters (7-24 days old) at 27°C using paired whole cell recordings. Laminar differences in synaptic efficacy were observed: excitatory connections were more secure than inhibitory connections in LII and inhibitory linkages in LII were less reliable than those in LIII-V. A majority of connections displayed paired-pulse facilitation or depression. Depression was observed for both EPSPs and IPSPs, but facilitation was seen almost exclusively for IPSPs. There were no frequency-dependent shifts between facilitation and depression. Synaptic depression was associated with an increased failure rate and decreased PSP half-width for a majority of connections. However, there were no consistent changes in failure rate or PSP time course at facilitating connections. IPSPs evoked at high-failure synapses had consistently smaller amplitude and showed greater facilitation than low-failure connections. Facilitation at inhibitory connections was positively correlated with synaptic jitter and associated with a decrease in latency. At many connections, the paired-pulse ratio varied from trial to trial and depended on the amplitude of the first PSP; dependence was greater for inhibitory synapses than excitatory synapses. Paired-pulse ratios for connections onto neurons with rapidly adapting, "phasic" discharge to depolarizing current injection were significantly greater than for connections onto neurons with tonic discharge properties. These results are evidence of diversity in synaptic transmission between dorsal horn neurons, the nature of which may depend on the types of linkage, laminar location, and intrinsic firing properties of postsynaptic cells.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Animals, Newborn; Bicuculline; Cricetinae; Electric Stimulation; Excitatory Amino Acid Antagonists; Female; GABA-A Receptor Antagonists; Glycine Agents; In Vitro Techniques; Lysine; Male; Mesocricetus; Neural Pathways; Patch-Clamp Techniques; Posterior Horn Cells; Reaction Time; Spinal Cord; Strychnine; Synapses; Synaptic Transmission; Time Factors

Transient electrical impulses are conventionally used to elicit physiological responses in excitable tissues. While electrical stimulation has many advantages, it requires an electrode-tissue interface, exhibits relatively low spatial selectivity and always produces a "stimulus artifact". Recently, it has been shown that pulsed, low-energy infrared laser light can evoke nerve, muscle and sensory responses similar to those induced by traditional electrical stimulation in a contact-free, damage-free, artifact-free and spatially selective manner. However, the effect of transient infrared laser light on neurotransmission in the CNS is still largely unknown. Here, we tested the effect of infrared laser light on GABAergic neurotransmission. We recorded spontaneous inhibitory postsynaptic currents (sIPSCs) from cultured rat cortical neurons prior to and after infrared laser stimulation. Using transient infrared laser light, we either stimulated the neuronal soma that had axonal projections to the recorded neuron or directly stimulated the axons that projected to the recorded neuron. Optical stimulation led to enhanced amplitude, decreased decay time constant and increased frequency of sIPSCs. These alterations of sIPSC properties produced by optical stimulation were specifically mediated by GABA(A) receptors and caused by the transient laser light per se since no exogenous substances such as caged compounds were used. These data show that optical stimulation using transient infrared laser light can alter GABAergic neurotransmission and demonstrate that it may be an alternative approach to electrical stimulation in studying GABAergic function.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Benzylamines; Bicuculline; Cells, Cultured; Cerebral Cortex; Dose-Response Relationship, Radiation; Embryo, Mammalian; Excitatory Amino Acid Antagonists; Female; GABA-A Receptor Antagonists; Inhibitory Postsynaptic Potentials; Lasers; Neurons; Patch-Clamp Techniques; Phosphinic Acids; Pregnancy; Rats; Synaptic Transmission; Temperature; Valine

Large aspiny neurons and most of the GABAergic interneurons survive transient cerebral ischemia while medium spiny neurons degenerate in 24 h. Expression of a long-term enhancement of excitatory transmission in medium spiny neurons but not in large aspiny neurons has been indicated to contribute to this selective vulnerability. Because neuronal excitability is determined by the counterbalance of excitation and inhibition, the present study examined inhibitory synaptic transmission in large aspiny neurons after ischemia in rats. Transient cerebral ischemia was induced for 22 min using the four-vessel occlusion method and whole-cell voltage-clamp recording was performed on striatal slices. The amplitudes of evoked inhibitory postsynaptic currents in large aspiny neurons were significantly increased at 3 and 24 h after ischemia, which was mediated by the increase of presynaptic release. Postsynaptic responses were depressed at 24 h after ischemia. Inhibitory postsynaptic currents could be evoked in large aspiny neurons at 24 h after ischemia, suggesting that they receive GABAergic inputs from the survived GABAergic interneurons. Muscimol, a GABA(A) receptor agonist, presynaptically facilitated inhibitory synaptic transmission at 24 h after ischemia. Such facilitation was dependent on the extracellular calcium and voltage-gated sodium channels. The present study demonstrates an enhancement of inhibitory synaptic transmission in large aspiny neurons after ischemia, which might reduce excitotoxicity and contribute, at least in part, to the survival of large aspiny neurons. Our data also suggest that large aspiny neurons might receive inhibitory inputs from GABAergic interneurons.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Biophysics; Biotin; Calcium; Choline O-Acetyltransferase; Corpus Striatum; Disease Models, Animal; Electric Stimulation; Excitatory Amino Acid Antagonists; GABA Agonists; GABA Antagonists; gamma-Aminobutyric Acid; Glutamate Decarboxylase; In Vitro Techniques; Ion Channel Gating; Ischemic Attack, Transient; Male; Membrane Potentials; Muscimol; Neurons; Ovulation Inhibition; Patch-Clamp Techniques; Rats; Rats, Wistar; Sodium Channel Blockers; Synaptic Transmission; Tetrodotoxin; Time Factors

Glutamine (GLN) is a precursor for synthesis of glutamate and gamma-aminobutyric acid (GABA) and has been found in the cerebrospinal fluid (CSF) at mean concentrations of 0.6 mM. Experiments on slices are usually performed in artificial CSF (aCSF) kept free of amino acids. Therefore, the role of glutamine, particularly in tissue of epileptic animals, remains elusive.. Using extracellular recordings we studied effects of GLN on field potentials and stimulus-evoked field responses in the medial entorhinal cortex (MEC) of combined entorhinal cortex hippocampal slices from pilocarpine-treated chronic epileptic rats and age-matched saline-injected control rats.. In presence of GLN (0.5 and 2 mM) recurrent epileptiform discharges (REDs) were observed in slices from epileptic rats (64% and 80%, respectively), but not in slices from control rats. REDs were restricted to the superficial MEC, suppressed by the alpha-Amino-3-hydroxy-5-methyl-4-isoxazol-propionate (AMPA)/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (30 microM), attenuated by the inhibitor of neuronal glutamine transporters methylamino-isobutyric acid (10 mM), and apparently augmented and prolonged by the GABA(A) receptor antagonist bicuculline-methiodide (5 microM). In contrast, amplitudes of stimulus evoked nonsynaptic and synaptic field responses increased in slices from control rats (+23% and +12% of the reference values) and insignificantly less or not in those of epileptic rats (+6.5% and -0.25%, respectively). Notably, stimulus-evoked slow negative transients confined to slices of epileptic animals were reduced in amplitude (-18%).. In combined entorhinal hippocampal slices from chronic epileptic animals, GLN induces glutamatergic REDs via neuronal uptake in superficial layers of the MEC where inhibitory function seemed to be partially preserved.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Aminoisobutyric Acids; Animals; Bicuculline; Disease Models, Animal; Entorhinal Cortex; Evoked Potentials; Excitatory Amino Acid Antagonists; GABA Antagonists; Glutamine; In Vitro Techniques; Male; Pilocarpine; Rats; Rats, Wistar; Status Epilepticus

The precise temporal control of neuronal action potentials is essential for regulating many brain functions. From the viewpoint of a neuron, the specific timings of afferent input from the action potentials of its synaptic partners determines whether or not and when that neuron will fire its own action potential. Tuning such input would provide a powerful mechanism to adjust neuron function and in turn, that of the brain. However, axonal plasticity of action potential timing is counter to conventional notions of stable propagation and to the dominant theories of activity-dependent plasticity focusing on synaptic efficacies.. Here we show the occurrence of activity-dependent plasticity of action potential propagation delays (up to 4 ms or 40% after minutes and 13 ms or 74% after hours) and amplitudes (up to 87%). We used a multi-electrode array to induce, detect, and track changes in propagation in multiple neurons while they adapted to different patterned stimuli in controlled neocortical networks in vitro. The changes did not occur when the same stimulation was repeated while blocking ionotropic gabaergic and glutamatergic receptors. Even though induction of changes in action potential timing and amplitude depended on synaptic transmission, the expression of these changes persisted in the presence of the synaptic receptor blockers.. We conclude that, along with changes in synaptic efficacy, propagation plasticity provides a cellular mechanism to tune neuronal network function in vitro and potentially learning and memory in the brain.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Bicuculline; Cerebral Cortex; Evoked Potentials; Hippocampus; Learning; Memory; Neuronal Plasticity; Neurons; Reaction Time; Synapses

The learned vocalizations of songbirds constitute a rhythmic behavior that is thought to be governed by a central pattern generator and that is accompanied by highly patterned neural activity. Phasic premotor activity is observed during singing in HVC [used as a proper name following the nomenclature of Reiner et al. (2004)], a telencephalic song system nucleus that is essential for song production. Moreover, HVC neurons display phasic patterns of auditory activity in response to song stimulation. To address the cellular basis of pattern generation in HVC, we investigated its rhythm-generating abilities. We report here the induction of sustained, rhythmic activity patterns in HVC when isolated in vitro. Brief, high-frequency stimulation evoked repetitive postsynaptic potentials (PSPs) and local field potentials (LFPs) from HVC neurons recorded in a brain slice preparation made from adult male zebra finches. These rhythmic events were sustained for seconds in the absence of ongoing, phasic stimulation, and they had temporal properties similar to those of syllable occurrence within zebra finch song. Paired recordings revealed synchrony between repetitive PSP and LFP occurrence, indicating that a population of cells participates in this patterned activity. The PSPs resulted from multiple, coordinated, fast-glutamatergic, synaptic inputs. Moreover, their occurrence and timing relied on inhibitory synaptic transmission. Thus, HVC itself has rhythmic abilities that could influence the timing of neural activity over relatively long time windows. These rhythmic properties may contribute to song production or perception in vivo.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Analysis of Variance; Animals; Bicuculline; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Finches; GABA Antagonists; In Vitro Techniques; Male; Models, Neurological; Neurons; Patch-Clamp Techniques; Periodicity; Picrotoxin; Prosencephalon; Reaction Time; Synaptic Transmission; Vocalization, Animal

During the early development of neocortical networks, many glutamatergic synapses lack AMPA receptors and are physiologically silent. We show in neocortical cultures that spontaneous synchronous network activity is able to convert silent synapses to active synapses by the incorporation of AMPA receptors into synaptic complexes throughout the network within a few minutes. To test the effect of synaptic activation on the connectivity of neuronal populations, we created separated neuronal networks that could innervate each other. We allowed outgrowing axons to invade the neighboring network either before or after the onset of synchronous network activity. In the first case, both subnetworks connected to each other and synchronized their activity, whereas in the second case, axonal connections failed to form and network activity did not synchronize between compartments. We conclude that early spontaneous synchronous network activity triggers a global AMPAfication of immature synapses, which in turn prevents later-arriving axons from forming afferent connections. This activity-dependent process may set the range of corticocortical connections during early network development before experience-dependent mechanisms begin elaborating the mature layout of the neocortical connections and modules.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Axons; Bicuculline; Calcium Signaling; Dextrans; Electric Stimulation; Embryo, Mammalian; Excitatory Amino Acid Antagonists; GABA Antagonists; Immunohistochemistry; Membrane Potentials; Neocortex; Nerve Net; Neural Pathways; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Rhodamines; Synapses; Synaptophysin; Time Factors

The hypothalamic hamartoma (HH) is a rare developmental malformation often characterized by gelastic seizures, which are usually refractory to medical therapy. The mechanisms of epileptogenesis operative in this subcortical lesion are unknown. In this study, we used standard patch-clamp electrophysiological techniques combined with histochemical approaches to study individual cells from human HH tissue immediately after surgical resection. More than 90% of dissociated HH cells were small (6-9 microm soma) and exhibited immunoreactivity to the neuronal marker NeuN, and to glutamic acid decarboxylase, but not to glial fibrillary acidic protein. Under current-clamp, whole-cell recordings in single dissociated cells or in intact HH slices demonstrated typical neuronal responses to depolarizing and hyperpolarizing current injection. In some cases, HH cells exhibited a "sag-like" membrane potential change during membrane hyperpolarization. Interestingly, most HH cells exhibited robust, spontaneous "pacemaker-like" action potential firing. Under voltage-clamp, dissociated HH cells exhibited functional tetrodotoxin (TTX)-sensitive Na(+) and tetraethylammonium-sensitive K(+) currents. Both GABA and glutamate evoked whole-cell currents, with GABA exhibiting a peak current amplitude 10-fold greater than glutamate. These findings suggest that human HH tissues, associated with gelastic seizures, contained predominantly small GABAergic inhibitory neurons that exhibited intrinsic "pacemaker-like" behavior.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Adolescent; Adult; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Anesthetics, Local; Bicuculline; Cadmium Chloride; Child; Child, Preschool; Drug Interactions; Electrophysiology; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; GABA Antagonists; gamma-Aminobutyric Acid; Glial Fibrillary Acidic Protein; Glutamate Decarboxylase; Glutamic Acid; Hamartoma; Humans; Hypothalamus; Immunohistochemistry; In Vitro Techniques; Infant; Isoenzymes; Kainic Acid; Male; Membrane Potentials; Neurons; Patch-Clamp Techniques; Periodicity; Phosphopyruvate Hydratase; Potassium Channel Blockers; Tetraethylammonium; Tetrodotoxin; Valine

In the cerebral cortex of mammals, gamma-aminobutyric acid (GABA)ergic neurons represent 15-25% of all neurons, depending on the species and area being examined. Because converging evidence suggests that activity may play an important role in the neuritic maturation and synaptic function of GABAergic neurons, it is feasible that activity plays a role in the regulation of the proportion of GABAergic neurons. Here we provide direct evidence that early in cortical development activity blockade may deplete the network of a subpopulation of GABA immunoreactive neurons characterized by their small size and late generation in vitro. In a period of time coinciding with the emergence of synchronous network activity, the survival and morphological differentiation of GABAergic neurons was influenced by long-term blockade of synaptic activity. While GABA(A) receptor antagonists had a minor promoting effect on interneuronal survival during the second week in vitro, antagonists of ionotropic glutamate receptors strongly impaired survival and differentiation of immature GABAergic interneurons. Interneuronal loss was more severe when N-methyl-D-aspartate receptors were blocked than after blockade of alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA)/kainate receptors. The decrease in the density of GABAergic neurons was irreversible, but could be prevented by the simultaneous addition of brain-derived neurotrophic factor (BDNF). These results suggest that there is a narrow time window during neocortical development when glutamatergic activity, and specially NMDA receptor stimulation, is crucial to assure survival and maturation of a subpopulation of late developing GABAergic interneurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Age Factors; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Apoptosis; Bicuculline; Calbindin 2; Calcium; Calcium-Binding Proteins; Cell Count; Cell Size; Cells, Cultured; Cerebral Cortex; Drug Interactions; Embryo, Mammalian; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; Glutamic Acid; Immunohistochemistry; In Situ Nick-End Labeling; Interneurons; Nerve Net; Parvalbumins; Picrotoxin; Rats; Rats, Sprague-Dawley; S100 Calcium Binding Protein G; Time Factors; Valine

Neurogenesis occurs throughout adult life in dentate gyrus of mammal hippocampus. Therefore, neurons at different stages of electrophysiological and morphological maturation and showing various, if any, synaptic inputs co-exist in the adult granule cell layer, as occurs during dentate gyrus development. The knowledge of functional properties of new neurons throughout their maturation can contribute to understanding their role in the hippocampal function. In this study electrophysiological and morphological features of granule layer cells, characterized as immature or mature neurons, without and with synaptic input, were comparatively described in adult rats. The patch-clamp technique was used to perform electrophysiological recordings, the occurrence of synaptic input evoked by medial perforant pathway stimulation was investigated and synaptic input was characterized. Cells were then identified and morphologically described via detection of biocytin injected through the patch pipette. The neuronal phenotype of recorded cells was assessed by immunohistochemistry and single-cell RT-PCR. Cells with very low capacitance, high input resistance, depolarized resting membrane potential and without synaptic activity were found exclusively at the border of the GCL facing hilus; this type of cell expressed the class III beta-tubulin neuronal marker (mRNA and protein) and did not express a glial marker. Immature neuronal cells with progressively increasing capacitance, decreasing input resistance and resting membrane potential getting more hyperpolarized showed only depolarizing GABAergic synaptic input at first and then also glutamatergic synaptic input. Finally, cells showing electrophysiological, synaptic, and morphological features of mature granule, expressing the mature neuron marker NeuN, were identified.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Calcium Channel Blockers; Carbocyanines; Cellular Senescence; Dentate Gyrus; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; GABA Antagonists; Glial Fibrillary Acidic Protein; Immunohistochemistry; In Vitro Techniques; Male; Membrane Potentials; Microscopy, Confocal; Neural Cell Adhesion Molecule L1; Neurons; Patch-Clamp Techniques; Perforant Pathway; Phosphopyruvate Hydratase; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sialic Acids; Synapses; Synaptic Transmission; Tetrodotoxin; Tubulin; Valine; Verapamil

Spontaneous activity was monitored during pharmacological blockade of GABA(A) receptor function in the CA1 minislice (CA3 was cut off). Synaptic inhibition was blocked by competitive GABA(A) antagonists bicuculline-methiodide (Bic) or GABAZINE (GBZ) and the chloride channel blocker picrotoxin (PTX). Extra- and intracellular recordings using sharp electrodes were carried out in stratum radiatum and pyramidale. At low antagonist concentrations (Bic, GBZ: 1-10 microM; PTX: < 100 microM), synchronized bursts (< 500 ms in duration, interictal activity) were seen as described previously. However, in the presence of high concentrations (Bic, GBZ: 50-100 microM; PTX: 100-200 microM), seizure-like, ictal events (duration 4-17 s) were observed in 67 of 88 slices. No other experimental measures to increase excitability were applied: cation concentrations ([Ca2+]o = 2 mM, [Mg2+]o = 1.7 mM, [K+]o = 3 mM) and recording temperature (30-32 degrees C) were standard and GABA(B)-mediated inhibition was intact. In whole-slice recordings prominent interictal activity, but fewer ictal events were observed. A reduced ictal activity was also observed when interictal-like responses were evoked by afferent stimulation. Ictal activity was reversibly blocked by antagonists of excitatory transmission, CNQX (40 microM) or D-AP5 (50 microM). Disinhibition-induced ictal development did not rely on group I mGluR activation as it was not prevented in the presence of group I mGluR antagonists (AIDA or 4CPG). (RS)-3,5-DHPG prevented the induction and reversed the tertiary component of the ictal event through a group I mGluR-independent mechanism.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Age Factors; Animals; Bicuculline; Epilepsy; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; Glycine; Guinea Pigs; Hippocampus; Neural Inhibition; Neurons, Afferent; Organ Culture Techniques; Picrotoxin; Pyridazines; Receptors, AMPA; Receptors, GABA-A; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Resorcinols

Changes in intracellular chloride concentration, mediated by chloride influx through GABA(A) receptor-gated channels, may modulate GABA(B) receptor-mediated inhibitory postsynaptic potentials (GABA(B) IPSPs) via unknown mechanisms. Recording from CA3 pyramidal cells in hippocampal slices, we investigated the impact of chloride influx during GABA(A) receptor-mediated IPSPs (GABA(A) IPSPs) on the properties of GABA(B) IPSPs. At relatively positive membrane potentials (near -55 mV), mossy fiber--evoked GABA(B) IPSPs were reduced (compared with their magnitude at -60 mV) when preceded by GABA(A) receptor--mediated chloride influx. This effect was not associated with a correlated reduction in membrane permeability during the GABA(B) IPSP. The mossy fiber--evoked GABA(B) IPSP showed a positive shift in reversal potential (from -99 to -93 mV) when it was preceded by a GABA(A) IPSP evoked at cell membrane potential of -55 mV as compared with -60 mV. Similarly, when intracellular chloride concentration was raised via chloride diffusion from an intracellular microelectrode, there was a reduction of the pharmacologically isolated monosynaptic GABA(B) IPSP and a concurrent shift of GABA(B) IPSP reversal potential from -98 to -90 mV. We conclude that in hippocampal pyramidal cells, in which "resting" membrane potential is near action potential threshold, chloride influx via GABA(A) IPSPs shifts the reversal potential of subsequent GABA(B) receptor--mediated postsynaptic responses in a positive direction and reduces their magnitude.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Chlorides; Electrophysiology; Excitatory Amino Acid Antagonists; GABA Antagonists; Male; Membrane Potentials; Mossy Fibers, Hippocampal; Neural Inhibition; Organophosphorus Compounds; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Receptors, GABA-B

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

Early visual experience is essential in the refinement of developing neural connections. In vivo whole-cell recording from the tectum of Xenopus tadpoles showed that repetitive dimming-light stimulation applied to the contralateral eye resulted in persistent enhancement of glutamatergic inputs, but not GABAergic or glycinergic inputs, on tectal neurons. This enhancement can be attributed to potentiation of retinotectal synapses. It required spiking of postsynaptic tectal cells as well as activation of NMDA receptors, and effectively occluded long-term potentiation (LTP) of retinotectal synapses induced by direct electrical stimulation of retinal ganglion cells. Thus, LTP-like synaptic modification can be induced by natural visual inputs and may be part of the underlying mechanism for the activity-dependent refinement of developing connections.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Dicarboxylic Acids; Light; Long-Term Potentiation; Neurons; Neurotransmitter Uptake Inhibitors; Photic Stimulation; Pyrrolidines; Retina; Superior Colliculi; Synapses; Visual Pathways; Visual Perception; Xenopus

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

Intracellular recordings in the guinea pig and cat basolateral amygdaloid (BL) complex maintained as slices in vitro revealed that a subpopulation of neurons (79%) in the lateral (AL) and basolateral (ABl) nuclei generated two types of slow oscillations of the membrane potential upon steady depolarization from resting potential. The cells were of a stellate or pyramidal-like shape and possessed spiny dendrites and an axon leaving the local synaptic environment, and thus presumably represented projection neurons. Similar oscillatory activity was observed in projection neurons of the cat AL nucleus recorded in vivo. Oscillatory activity with a low threshold of activation (low-threshold oscillation, LTO) appeared as rhythmic deflections (amplitudes, 2-6 mV) of the membrane potential positive to -60 mV. Fast Fourier transformation (FFT) demonstrated a range of frequencies of LTOs between 0.5 and 9 Hz, with >80% occurring at 1-3.5 Hz and an average at 2.3 +/- 1.1 Hz. LTOs were more regular after pharmacological blockade of synaptic transmission and were blocked by tetrodotoxin (TTX). Blockade of LTOs and Na+ spikes revealed a second type of oscillatory activity (high-threshold oscillation, HTO) at depolarizations beyond -40 mV, which was capable of triggering high-threshold spikes. HTOs ranged between 1 and 7.5 Hz, with >80% occurring at 2-6 Hz and an average at 5.8 +/- 1.1 Hz. HTOs vanished at a steady membrane polarization positive to -20 mV. Current versus voltage relations obtained under voltage-clamp conditions revealed two regions of negative slope conductance at -55 to -40 mV and at around -30 mV, which largely overlapped with the voltage ranges of LTOs and HTOs. TTX abolished the first region of negative slope conductance (-55 to -40 mV) and did not significantly influence the second region of negative slope conductance. Neuronal responses to maintained depolarizing current pulses consisted of an initial high-frequency discharge (up to 100 Hz), the frequency of which depended on the amplitude of the depolarizing current pulse, followed by a progressive decline ("adaptation") toward a slow-rhythmic firing pattern. The decay in firing frequency followed a double-exponential function, with time constants averaging 57 +/- 28 ms and 3.29 +/- 1.85 s, and approached steady-state frequencies at 6.3 +/- 2.9 Hz (n = 17). Slow-rhythmic firing remained at this frequency over a wide range of membrane polarization between approximately -50 and -20 mV, although indiv

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Amygdala; Animals; Bicuculline; Cats; GABA Antagonists; Guinea Pigs; In Vitro Techniques; Indoles; Membrane Potentials; Neurons; Organophosphorus Compounds; Oscillometry; Patch-Clamp Techniques; Scopolamine; Serotonin Antagonists; Tetrodotoxin; Tropisetron

The spontaneous, synchronous activity induced by 4-aminopyridine (4AP, 50 microM) in the adult rat entorhinal cortex was analyzed with simultaneous field potential and intracellular recordings in an in vitro slice preparation. Four-AP induced isolated negative-going field potentials (interval of occurrence = 27.6 +/- 9.9 (SD) s; n = 27 slices) that corresponded to intracellular long-lasting depolarizations (LLDs), and ictallike epileptiform discharges (interval of occurrence = 10.4 +/- 5.7 min; n = 27 slices) that were initiated by the negative field potentials. LLDs recorded with K-acetate-filled microelectrodes triggered few action potentials of variable amplitude and had a duration of 1.7 +/- 0.8 s (n = 26 neurons), a peak amplitude of 11.8 +/- 5.0 mV (n = 26 neurons) and a reversal potential of -66.2 +/- 3.9 mV (n = 17 neurons). The ictal discharges studied with K-acetate microelectrodes consisted of prolonged depolarizations (duration = 72.9 +/- 44.3 s; peak amplitude = 29.2 +/- 11.4 mV; n = 25 neurons) with action-potential firing during both the tonic and the clonic phase. These depolarizations had a reversal potential of -45.3 +/- 3.8 mV (n = 4 neurons). Intracellular Cl- diffusion from KCl-filled microelectrodes made both LLDs and ictal depolarizations increase in amplitude (30.5 +/- 8.2 mV, n = 8 and 41.8 +/- 9.8 mV, n = 6 neurons, respectively). LLDs recorded with KCl and 2-(trimethyl-amino)N-(2, 6-dimethylphenyl)-acetamide (QX-314) microelectrodesreached an amplitude of 36.3 +/- 5.2 mV, lasted 12.5 +/- 6.5 s, and had a reversal potential of -31.3 +/- 2.5 mV (n = 4 neurons); under these recording procedures the ictal discharge amplitude was 41.5 +/- 5.0 mV and the reversal potential -24.0 +/- 7.0 mV (n = 4 neurons). The N-methyl-D-aspartate (NMDA) receptor antagonist 3,3-(2-carboxy-piperazine-4-yl)-pro-pyl-l-phosphonate (10 microM, n = 5 neurons) alone or concomitant with the nonNMDA receptor antagonist 6-cyano-7-nitro-quinoxaline-2,3-dione (10 microM, n = 4 neurons) abolished ictal discharges, without influencing LLDs. LLDs were blocked by the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline methiodide (BMI, 10 microM, n = 6 neurons) or the mu-opioid receptor agonist (-Ala2-N-Me-Phe, Gly-ol) enkephalin (DAGO, 10 microM, n = 2 neurons). Application of BMI (n = 4 neurons) or DAGO (n = 2 neurons) to control the medium abolished LLDs and ictal discharges but disclosed a novel type of epileptiform depolarization that lasted 3.5 +/-

Topics: 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Bicuculline; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; In Vitro Techniques; Lidocaine; Male; Membrane Potentials; Neurons; Potassium Acetate; Rats; Rats, Sprague-Dawley; Receptors, GABA-A

The dynamic clamp technique was used in thalamocortical neurons of the rat and cat dorsal lateral geniculate nucleus in vitro to investigate the effects of the hyperpolarization-activated cation current, Ih, and of its neuromodulation on burst firing and delta oscillations. Specific block of endogenous Ih using 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino)pyridinium chloride (ZD7288) (300 microM) abolished the depolarizing "sag" response to negative current steps, markedly increased the latency and shortened the duration of the low-threshold Ca2+ potentials, and decreased the number of action potentials in the burst evoked by the low-threshold Ca2+ potential. Subsequent introduction of artificial Ih using the dynamic clamp re-instated the "sag" and all the original properties of the low-threshold Ca2+ potential. In the absence of ZD7288, introduction of artificial outward Ih with the intention of abolishing endogenous Ih removed the depolarizing "sag" and produced similar effects on the low-threshold Ca2+ potentials as those observed during the pharmacological block of Ih. Application of ZD7288 to thalamocortical neurons displaying delta oscillations led to a reduction in the voltage range of their existence or to a complete cessation of this behaviour. A subsequent introduction of artificial Ih re-enabled the generation of delta oscillations. In the presence of ZD7288, physiologically relevant positive shifts in the voltage-dependence of artificial Ih increased the amplitude and duration of the low-threshold Ca2+ potential and increased the likelihood of delta oscillations while negative shifts had opposite effects. These results highlight the important difference between the dependence of burst firing and oscillations on membrane potential and their dependence on the properties of Ih, and demonstrate that the modulation by Ih of low-threshold Ca2+ potentials and burst firing in thalamocortical neurons, as well as the ability of these neurons to generate delta oscillations, is more elaborate than previously described.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Bicuculline; Cardiovascular Agents; Cats; Cerebral Cortex; Excitatory Amino Acid Antagonists; Female; GABA Antagonists; Geniculate Bodies; In Vitro Techniques; Male; Neurons; Organophosphorus Compounds; Patch-Clamp Techniques; Periodicity; Pyrimidines; Rats; Rats, Wistar; Sleep; Thalamus; Wakefulness

Entorhinal cortex layer III cells send their axons into hippocampal area CA1, forming the less well studied branch of the perforant path. Using electrophysiological and morphological techniques within a slice preparation, we can classify medial entorhinal cortex layer III cells into four different types. Type 1 and 2 cells were projection cells. Type 1 cells fired regularly and possessed high input resistances and long membrane time constants. Electrical stimulation of the lateral entorhinal cortex revealed a strong excitation by both N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor-mediated excitatory postsynaptic potentials. Type 2 cells accommodated strongly, had lower input resistances, faster time constants and featured prominent synaptic inhibition. Type 1 and 2 cells responded to repetitive synaptic stimulation with a prolonged hyperpolarization. We identified the two other, presumed local circuit, cell types whose axons remained within the entorhinal cortex. Type 3 cells were regular firing, had high input resistances and slow membrane time constants, while type 4 cells fired at higher frequencies and possessed a faster time constant and lower input resistance than type 3 neurons. Type 3 cells presented long-lasting excitatory synaptic potentials. Type 4 neurons were the only ones with different responses to stimulation from different sites. Upon lateral entorhinal cortex stimulation they responded with an excitatory postsynaptic potential, while a monosynaptic inhibitory postsynaptic potential was evoked from deep layer stimulation. In contrast to type 1 and 2 neurons, none of the local circuit cells could be antidromically activated from deep layers, and prolonged hyperpolarizations following synaptic repetitive stimulation were also absent in these cells. Together, the complementing morphology and the electrophysiological characteristics of all the cells can provide the controlled flexibility required during the transfer of cortical information to the hippocampus.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Electric Stimulation; Entorhinal Cortex; Excitatory Amino Acid Antagonists; Female; GABA Antagonists; In Vitro Techniques; Membrane Potentials; Neurons; Organophosphorus Compounds; Phosphinic Acids; Propanolamines; Quinoxalines; Rats; Rats, Wistar; Receptors, GABA-A; Receptors, GABA-B; Synaptic Transmission

Blockade of gamma-aminobutyric acid (GABAA) receptors in the anterior basolateral amygdala (BLA) with bicuculline methiodide results in an increase in heart rate, blood pressure and "anxiety" in rats. Glutamate receptors in the BLA are also reported to be involved in eliciting anxiety responses. The purpose of this study was to investigate the interaction between GABAergic inhibition and glutamatergic excitation in the BLA. Male Wistar rts were implanted with femoral arterial catheters and bilateral chronic microinjection cannulae into the BLA. Each animal was injected with either artificial cerebrospinal fluid (100 nl), bicuculline methiodide (10 pmol/100 nl) or bicuculline methiodide + one dose of an antagonist of either the N-methyl-D-aspartate receptor [AP5 (20 and 100 pmol) and dizocilpine (25 and 125 pmol)] or the non-N-methyl-D-aspartate ionotropic receptor [CNQX (10 and 50 pmol) and GYKI 52466 (50 and 250 pmol)]. Increases in heart rate, blood pressure and "anxiety" (as measured in the social interaction test) observed in rats after bicuculline methiodide injections into the BLA were blocked in a dose dependent manner with the concurrent injections of either N-methyl-D-aspartate or non-N-methyl-D-aspartate antagonists, suggesting that activation of both subtypes of glutamate ionotropic receptors may be necessary for the responses elicited by GABAA receptor blockade in the basolateral amygdala.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amygdala; Animals; Anti-Anxiety Agents; Anxiety; Benzodiazepines; Bicuculline; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; Hemodynamics; Male; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

Repetitive local application of a short train of stimuli to the rat substantia nigra and ventral tegmental area elicited a predominant depolarizing, slow, long-lasting synaptic response in the dopaminergic cells intracellularly recorded in vitro. This slow excitatory postsynaptic potential ranged between 13 and 27 mV at holding potentials of about-75 mV and lasted for 0.2-6 s. It was not greatly affected by the perfusion of 6-cyano-7-nitroquinoxaline-2,3-dione (10-20 microM), while it was potentiated in the presence of bicuculline methiodide (30 microM) or picrotoxin (50-100 microM) and 2-hydroxysaclofen (100-300 microM). In contrast, a substantial component of the slow excitatory postsynaptic potential was reversibly depressed, in a concentration-dependent manner, by the application of the N-methyl-D-aspartate receptor antagonists D,1-2-amino-5-phosphonovalerate (10-100 microM). Furthermore, the slow excitatory postsynaptic potential was reversibly increased by the superfusion of nominally magnesium-free solution. It was graded, increasing in amplitude with increased stimulus intensity, and was blocked by tetrodotoxin (0.5 microM). We suggest that a sustained activation of synaptic terminals containing excitatory amino acids mediates a slow excitatory postsynaptic potential in the dopaminergic cells of the midbrain. N-Methyl-D-aspartate receptors participate in the generation of this slow potential, while the alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate/kainate receptors do not seem to contribute substantially to this potential. This N-methyl-D-aspartate-mediated synaptic event could be implicated in the release of dopamine as well as in the excitotoxic injury of the dopaminergic neurons.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Dopamine; Electric Stimulation; Evoked Potentials; Excitatory Amino Acid Antagonists; In Vitro Techniques; Ketamine; Membrane Potentials; Mesencephalon; Neurons; Picrotoxin; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Substantia Nigra; Synapses; Synaptic Transmission; Tegmentum Mesencephali; Tetrodotoxin; Time Factors

1. Glutamatergic excitation and gamma-aminobutyric acid (GABA)-ergic inhibition in layers II and III of the auditory cortex of anaesthetized guinea-pigs were recorded optically using a voltage-sensitive dye RH795 and a 12 x 12 photodiode array. 2. After contralateral ear stimulation with pure tones, transient excitatory responses followed by inhibitory responses were observed in fields A (primary) and DC of the auditory cortex. The area of the excitatory responses was sandwiched or surrounded by the areas of the inhibitory responses. 3. Optically recorded excitatory responses to pure tones had two components: a component sensitive to 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-N-methyl-D-aspartate (non-NMDA) receptor antagonist, and a component sensitive to 2-amino-5-phosphono-valerate (APV), an NMDA receptor antagonist. Application of CNQX (5 microM) to the auditory cortex suppressed an early, but not a late, phase of the excitation; application of APV (100 microM) had the opposite effect. Concomitant application of CNQX and bicuculline methiodide (BMI, 4 microM), a GABAA receptor antagonist, increased the amplitude of the late phase 4-fold. This enhanced response was suppressed by APV. 4. These results indicate that (i) auditory cortical excitatory responses are mediated by both non-NMDA and NMDA receptors, (ii) inhibition is mediated by GABAA receptors, (ii) the excitatory bands are sandwiched or surrounded by GABAA receptor-mediated inhibitory areas and (iv) GABAA receptors effectively inhibit the NMDA, but not the non-NMDA, receptor-mediated excitation.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Acoustic Stimulation; Animals; Auditory Cortex; Bicuculline; Excitatory Amino Acid Antagonists; GABA Antagonists; Guinea Pigs; Models, Biological; Receptors, GABA; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Synapses

Whole-cell recordings in hypothalamic slices from immature rats were used to test the hypothesis that inhibitory and excitatory amino acid neurotransmitters mediate fast synaptic currents in the medial preoptic area (MPOA). Bicuculline methiodide reversibly blocked spontaneous inhibitory postsynaptic currents (IPSCs), and 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNQX) blocked spontaneous excitatory postsynaptic currents (EPSCs). These competitive antagonists act at gamma-aminobutyric acid (GABA)A and non-N-methyl-D-aspartate (NMDA) glutamate receptors, respectively, thus supporting the hypothesis that these amino acid receptors activate most if not all fast synaptic currents in the MPOA.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Evoked Potentials; Excitatory Amino Acids; Female; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid; In Vitro Techniques; Male; Neurons; Patch-Clamp Techniques; Preoptic Area; Rats; Rats, Sprague-Dawley; Synapses; Synaptic Transmission

The maturation of retinogeniculate excitatory transmission and intrathalamic inhibition was studied in slices of the dorsal LGN obtained from ferrets during the first 2 postnatal months. Response to optic tract stimulation at neonatal ages consisted of slow EPSPs lasting several hundred milliseconds. Application of the NMDA receptor antagonist D-(-)-2-amino-5-phosphonovaleric acid (D-APV) during the first 2 postnatal weeks resulted in EPSPs that were reduced in peak amplitude and dramatically curtailed in duration, indicating that NMDA receptors participate strongly in retinogeniculate transmission at the immature synapse. Gradually, EPSPs became shorter in duration such that after the second postnatal week, the retinogeniculate EPSPs were only a few milliseconds in duration. At this late stage of development responses were remarkably less affected by application of D-APV. These changes in contribution of NMDA receptors to retinogeniculate transmission were found to be due to the development of strong IPSPs, the result of gradual maturation of activation of GABAergic inhibition. Indeed, application of bicuculline methiodide to block GABAA receptor-mediated IPSPs strongly enhanced the NMDA component of the EPSPs in more mature cells. The voltage dependence and kinetics of NMDA-induced excitatory postsynaptic currents (NMDA EPSCs) were characterized by voltage-clamp recordings after blocking AMPA/kainate receptors with 6-cyano-7-nitroquinoxaline-2,3-dione and GABAA receptors wit' bicuculline methiodide. The voltage dependence of the NMDA EPSCs remained unaltered with age. During the first postnatal month the kinetic properties of the NMDA EPSCs also remained unaltered, but a reduction in EPSC duration was observed within the following weeks, well after the critical period of anatomical reorganization.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Afferent Pathways; Aging; Animals; Bicuculline; Electric Stimulation; Evoked Potentials; Ferrets; Geniculate Bodies; In Vitro Techniques; Kinetics; Neurons; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Retina; Synapses; Synaptic Transmission; Time Factors; Visual Pathways

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

Many studies suggest that the dentate gyrus (DG) is a control point for hippocampal epileptogenesis. However, the importance of GABAergic inhibition in the DG is not quite clear. Intracellular recordings were obtained from granule cells (GC) of the rat DG. In addition to GABAA-mediated spontaneous postsynaptic potentials (PSPs), some GC exhibited spontaneous slow hyperpolarizations (SH). The SH were more commonly observed in a high concentration of external potassium. 2-Hydroxysaclofen, a GABAB antagonist, reduced the SH. Focal stimulation of the perforant path (PP) in the subiculum with a single pulse evoked a depolarization followed by a SH, which were both abolished by the excitatory amino acid (EAA) blockers, 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) and 2-amino-5-phosphonovaleric acid (APV). When evoked with a train of pulses, the SH was unaffected by the EAA blockers in 40% of the cells, suggesting either the existence of a GABAergic PP, or an unidentified polysynaptic mechanism. In control, the synaptic response to PP stimulation was superficially similar whether the stimulus was applied in the subiculum or stratum moleculare. However, in presence of bicuculline, the subicular PSP was followed by a train of PSPs occurring at a constant frequency of 25 Hz. This 'reverberating' effect of bicuculline was decreased in presence of APV and was abolished in slices in which the excitatory transmission had been interrupted downstream from CA3 neurons, suggesting that reverberation required the integrity of the hippocampo-entorhinal loop. By contrast, bicuculline decreased the amplitude of the stratum moleculare PSP. It is concluded that GC receive tonic inhibition from GABA acting at GABAA and GABAB receptors. The role of GABAB receptors is unclear; by contrast, GABAA-mediated inhibition prevents GC from reverberated excitation. The probability of occurrence of reverberation is higher during activation of the whole temporo-ammonic pathway and is partly dependent on the activation of N-methyl-D-aspartate (NMDA) receptors. Thus, the in vitro brain slice can be used as a model to study reverberation which has been recently demonstrated to underlie epileptiform discharges in the whole brain preparation.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Baclofen; Bicuculline; Electric Stimulation; Epilepsy; Evoked Potentials; gamma-Aminobutyric Acid; Hippocampus; In Vitro Techniques; Male; Membrane Potentials; Pyramidal Tracts; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Receptors, GABA-B; 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

1. A slice preparation was used to study layer III field potentials (FPs) evoked by electrical stimulation of the white matter-layer VI border and their potentiation by patterned stimuli. 2. The dependence of the FP on recording position was investigated. The maximum field was recorded in layer III at a position radial to the site of stimulation. Because this negative FP reflects an excitatory synaptic current sink, this site was chosen for all subsequent experiments. 3. Under normal recording conditions, components of the layer III FP with latencies greater than 3 ms were completely abolished by kynurenate but unaffected by 2-amino-5-phosphonovalerate (AP5), indicating that this potential reflects the activation of non-NMDA excitatory amino acid receptors. 4. Addition of the gamma-aminobutyric acid (GABA)A receptor antagonist bicuculline methiodide (BMI) broadened the field potential and revealed an AP5-sensitive component. By filling the recording pipette with BMI, it was possible to substantially reduce inhibition locally around the recording site while avoiding stimulus-driven and spontaneous epileptiform activity. 5. Tetanic stimulation elicited a long-term potentiation (LTP) of the FP in 14 of 17 experiments when the BMI-filled pipette method was used. 6. Addition of 100 microM D,L-AP5 significantly reduced the average probability and magnitude of LTP. Nonetheless, in 2 of 8 experiments, significant LTP was observed after a tetanus in the presence of AP5. Control experiments confirmed that this concentration of AP5 was sufficient to maximally block cortical NMDA receptors. 7. We conclude that LTP of layer III field potentials can be reliably elicited, provided that GABAA-receptor mediated inhibition is blocked locally at the site of recording and that NMDA receptors are recruited during the conditioning stimulation. However, activation of NMDA receptors is apparently not an obligatory step for the induction of use-dependent increases in synaptic strength in the kitten striate cortex.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Analysis of Variance; Animals; Bicuculline; Cats; Electric Stimulation; Evoked Potentials; GABA-A Receptor Antagonists; Hippocampus; In Vitro Techniques; Kynurenic Acid; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Regression Analysis; Visual Cortex

The NMDA receptor-mediated component of the hippocampal granule cell population excitatory postsynaptic potential response to low frequency (< 0.2 Hz) stimulation of the medial perforant path was characterized in vivo. Extracellular recordings were obtained from the dentate molecular layer in anesthetized rabbits, and glutamatergic and GABAergic antagonists were applied locally by pressure ejection. To measure the NMDA-mediated component, the NMDA receptor antagonist D-5-aminophosphonovalerate (APV) was applied during the constant ejection of physiological saline, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and/or bicuculline methiodide. In general agreement with the results of attempts by other investigators to identify NMDA responses in vivo, APV did not significantly reduce the response to a single stimulus impulse in the presence of saline. However, an NMDA-mediated response was revealed when alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprianate receptor-mediated current flow was eliminated by applying the non-NMDA receptor antagonist CNQX. The NMDA component was negative-going as predicted, but its duration was considerably less than indicated in other studies of the dentate in vitro. The relative magnitudes of the NMDA and non-NMDA components of the EPSP were found to vary as a function of stimulus intensity or frequency. The NMDA receptor-mediated component represented 12% of the control response and increased to over 25% in response to higher stimulus intensities. A brief, high-frequency burst of impulses evoked a larger NMDA component in the presence of CNQX and was able to evoke an NMDA component in the presence of saline. Surprisingly, short trains of stimulation at lower frequencies typically produced suppression of the NMDA component. In a final series of experiments, it was found that many characteristics of the NMDA component were substantially altered by GABAergic inhibition. In the presence of the GABAA antagonist bicuculline, the magnitude of NMDA receptor-mediated responses was increased and their duration was greatly extended. Additionally, in the presence of bicuculline, the NMDA component facilitated markedly in response to frequencies of stimulus input > 20 Hz. These results indicate in vivo that the initiation and duration of NMDA current flow depend strongly upon the intensity and frequency of perforant path stimulation. In addition, the NMDA response to a single impulse appears to be reduced and truncated by input from GABAA rec

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Drug Interactions; Electric Stimulation; Evoked Potentials; Hippocampus; Infusions, Parenteral; Male; Quinoxalines; Rabbits; Receptors, N-Methyl-D-Aspartate; Synapses

We have previously shown that microinjection of drugs that impair gamma-aminobutyric acid (GABA)-mediated synaptic inhibition into the dorsomedial hypothalamus (DMH) of rats generates cardiovascular and behavioral changes that mimic the response to stress. The purpose of this study was to examine the role of excitatory amino acid (EAA) receptors in the DMH in generating the cardiovascular changes caused by withdrawal of local GABAergic inhibition in urethan-anesthetized rats. Local treatment of the DMH with the nonselective EAA antagonist kynurenic acid blocked or reversed the increases in heart rate and blood pressure caused by microinjection of the GABAA antagonists bicuculline methiodide (BMI) or picrotoxin into the same region. Conversely, similar injection of xanthurenic acid, a structural analogue of kynurenic acid without significant effects on EAA receptors, did not significantly alter the cardiovascular changes produced by either GABAA antagonist. The tachycardic effects of BMI were also attenuated by injection of either the N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonopentanoic acid or the non-NMDA EAA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. When the two EAA receptor antagonists were combined, their effects to suppress the BMI-induced tachycardia were additive. These findings suggest that the cardiovascular effects caused by blockade of GABAergic inhibition in the DMH of the rat are dependent on activation of local NMDA and non-NMDA EAA receptors.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Bicuculline; Blood Pressure; Dose-Response Relationship, Drug; gamma-Aminobutyric Acid; Heart Rate; Hypothalamus; Kynurenic Acid; Male; Picrotoxin; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, Amino Acid; Receptors, Cell Surface

Intracellular recordings were made from neurons of the zebra finch song control nucleus, the robust nucleus of the archistriatum (RA), in slice preparations to examine synaptic responses. RA neurons receive two separate inputs from the lateral magnocellular nucleus of the anterior neostriatum (1MAN) and the caudal nucleus of the ventral hyperstriatum (HVc). Excitatory postsynaptic potentials (EPSPs) elicited by stimulation of the fibers of the 1MAN were greatly reduced by 2-amino-5-phosphonopentanoic acid in many cells, whereas EPSPs elicited by stimulation of the fibers of the HVc were greatly reduced by 6-cyano-7-nitroquinoxaline-2,3-dione in all cells. It is concluded that RA neurons receive inputs mediated mostly by N-methyl-D-aspartate (NMDA) receptors from the 1MAN, and inputs mediated mostly by non-NMDA receptors from the HVc.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Birds; Brain; Electric Stimulation; Evoked Potentials, Somatosensory; gamma-Aminobutyric Acid; In Vitro Techniques; Male; Neurons; Picrotoxin; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Synapses; Vocalization, Animal

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