Showing papers on "Kainate receptor published in 1997"
TL;DR: The findings suggest that ketamine may disrupt dopaminergic neurotransmission in the PFC as well as cognitive functions associated with this region, in part, by increasing the release of glutamate, thereby stimulating postsynaptic non-NMDA glutamate receptors.
Abstract: Subanesthetic doses of ketamine, a noncompetitive NMDA receptor antagonist, impair prefrontal cortex (PFC) function in the rat and produce symptoms in humans similar to those observed in schizophrenia and dissociative states, including impaired performance of frontal lobe-sensitive tests. Several lines of evidence suggest that ketamine may impair PFC function in part by interacting with dopamine neurotransmission in this region. This study sought to determine the mechanism by which ketamine may disrupt dopaminergic neurotransmission in, and cognitive functions associated with, the PFC. A thorough dose-response study using microdialysis in conscious rats indicated that low doses of ketamine (10, 20, and 30 mg/kg) increase glutamate outflow in the PFC, suggesting that at these doses ketamine may increase glutamatergic neurotransmission in the PFC at non-NMDA glutamate receptors. An anesthetic dose of ketamine (200 mg/kg) decreased, and an intermediate dose of 50 mg/kg did not affect, glutamate levels. Ketamine, at 30 mg/kg, also increased the release of dopamine in the PFC. This increase was blocked by intra-PFC application of the AMPA/kainate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione CNQX. Furthermore, ketamine-induced activation of dopamine release and impairment of spatial delayed alternation in the rodent, a PFC-sensitive cognitive task, was ameliorated by systemic pretreatment with AMPA/kainate receptor antagonist LY293558. These findings suggest that ketamine may disrupt dopaminergic neurotransmission in the PFC as well as cognitive functions associated with this region, in part, by increasing the release of glutamate, thereby stimulating postsynaptic non-NMDA glutamate receptors.
1,697 citations
TL;DR: The cloning of GABAB receptors is reported and photoaffinity labelling experiments suggest that the cloned receptors correspond to two highly conserved GABAB receptor forms present in the vertebrate nervous system.
Abstract: GABA (gamma-amino-butyric acid), the principal inhibitory neurotransmitter in the brain, signals through ionotropic (GABA(A)/ GABA(c)) and metabotropic (GABA(B)) receptor systems. Here we report the cloning of GABA(B) receptors. Photoaffinity labelling experiments suggest that the cloned receptors correspond to two highly conserved GABA(B) receptor forms present in the vertebrate nervous system. The cloned receptors negatively couple to adenylyl cyclase and show sequence similarity to the metabotropic receptors for the excitatory neurotransmitter L-glutamate.
1,024 citations
TL;DR: GRIP is a new member of the PDZ domain-containing protein family which has seven PDZ domains and no catalytic domain and appears to serve as an adapter protein that links AMPA receptors to other proteins and may be critical for the clustering of AMPA receptor at excitatory synapses in the brain.
Abstract: AMPA glutamate receptors mediate the majority of rapid excitatory synaptic transmission in the central nervous system and play a role in the synaptic plasticity underlying learning and memory. AMPA receptors are heteromeric complexes of four homologous subunits (GluR1-4) that differentially combine to form a variety of AMPA receptor subtypes. These subunits are thought to have a large extracellular amino-terminal domain, three transmembrane domains and an intracellular carboxy-terminal domain. AMPA receptors are localized at excitatory synapses and are not found on adjacent inhibitory synapses enriched in GABA(A) receptors. The targeting of neurotransmitter receptors, such as AMPA receptors, and ion channels to synapses is essential for efficient transmission. A protein motif called a PDZ domain is important in the targeting of a variety of membrane proteins to cell-cell junctions including synapses. Here we identify a synaptic PDZ domain-containing protein GRIP (glutamate receptor interacting protein) that specifically interacts with the C termini of AMPA receptors. GRIP is a new member of the PDZ domain-containing protein family which has seven PDZ domains and no catalytic domain. GRIP appears to serve as an adapter protein that links AMPA receptors to other proteins and may be critical for the clustering of AMPA receptors at excitatory synapses in the brain.
879 citations
TL;DR: Determining the mechanisms underlying the development of this 'ménage à trois' will shed light not only on the wide range of trophic roles of glutamate and GABA in the developing brain, but also on the significance of the transition from neonatal to adult forms of plasticity.
817 citations
TL;DR: It is suggested that a number of G protein-coupled receptors activate the same class of postsynaptic K+ channel, which contains GIRK2, and that the same receptor can couple to different effector systems according to its subcellular location in the neuron.
735 citations
TL;DR: In this article, α-Actinin-2, a member of the spectrin/dystrophin family of actin-binding proteins, is identified as a brain postsynaptic density protein that colocalizes in dendritic spines with NMDA receptors and the putative NMDA receptor-clustering molecule PSD-95.
Abstract: The mechanisms by which neurotransmitter receptors are immobilized at postsynaptic sites in neurons are largely unknown. The activity of NMDA (N-methyl-D-aspartate) receptors is mechanosensitive1 and dependent on the integrity of actin2, suggesting a functionally important interaction between NMDA receptors and the postsynaptic cytoskeleton. α-Actinin-2, a member of the spectrin/dystrophin family of actin-binding proteins, is identified here as a brain postsynaptic density protein that colocalizes in dendritic spines with NMDA receptors and the putative NMDA receptor-clustering molecule PSD-95. α-Actinin-2 binds by its central rod domain to the cytoplasmic tail of both NR1 and NR2B subunits of the NMDA receptor, and can be immunoprecipitated with NMDA receptors and PSD-95 from rat brain. Intriguingly, NR1-α-actinin binding is directly antagonized by Ca2+/calmodulin. Thus α-actinin may play a role in both the localization of NMDA receptors and their modulation by Ca2+.
581 citations
TL;DR: It is reported that repetitive activation of the hippocampal mossy fibre pathway, which is associated with high-affinity kainate binding and many of the kainATE receptor subtypes, generates a slow excitatory synaptic current with all of the properties expected of a kainates receptor.
Abstract: Glutamate, the neurotransmitter at most excitatory synapses in the brain, activates a variety of receptor subtypes that can broadly be divided into ionotropic (ligand-gated ion channels) and metabotropic (G-protein-coupled) receptors. Ionotropic receptors mediate fast excitatory synaptic transmission, and based on pharmacological and molecular biological studies are divided into NMDA and non-NMDA subtypes. The non-NMDA receptor group is further divided into AMPA and kainate subtypes. Virtually all fast excitatory postsynaptic currents studied so far in the central nervous system are mediated by the AMPA and NMDA subtypes of receptors. Surprisingly, despite extensive analysis of their structure, biophysical properties and anatomical distribution, a synaptic role for kainate receptors in the brain has not been found. Here we report that repetitive activation of the hippocampal mossy fibre pathway, which is associated with high-affinity kainate binding and many of the kainate receptor subtypes, generates a slow excitatory synaptic current with all of the properties expected of a kainate receptor. This activity-dependent synaptic current greatly augments the excitatory drive of CA3 pyramidal cells.
533 citations
TL;DR: It is suggested that the single-channel conductance of certain recombinant AMPA receptors may be determined by the expression of edited GluR2 subunits in neurons.
Abstract: Non-NMDA glutamate receptor subunits of the AMPA-preferring subfamily combine to form ion channels with heterogeneous functional properties. We have investigated the effects of RNA editing at the Q/R site, splice variation of the “flip/flop” cassette, and multimeric subunit assembly on the single-channel conductance and kinetic properties of the recombinant AMPA receptors formed from GluR2 and GluR4 expressed in HEK 293 cells. We found that AMPA receptor single-channel conductance was dependent on the Q/R site editing state of the subunits comprising the channel. Calcium-permeable (unedited) channels had resolvable single-channel events with main conductance states of 7–8 pS, whereas fully edited GluR2 channels had very low conductances of ∼300 fS (estimated from noise analysis). Additionally, the flip splice variant of GluR4 conferred agonist-dependent conductance properties reminiscent of those found for a subset of AMPA receptors in cultured cerebellar granule cells. These results provide a description of the single-channel properties of certain recombinant AMPA receptors and suggest that the single-channel conductance may be determined by the expression of edited GluR2 subunits in neurons.
505 citations
Journal Article•
TL;DR: It is demonstrated that Ro 25-6981 is a highly selective, activity-dependent blocker of NMDA receptors that contain the NR2B subunit, which indicated a >5000-fold selectivity.
Abstract: The interaction of Ro 25-6981 with N-methyl-D-aspartate (NMDA) receptors was characterized by a variety of different tests in vitro. Ro 25-6981 inhibited 3H-MK-801 binding to rat forebrain membranes in a biphasic manner with IC50 values of 0.003 microM and 149 microM for high- (about 60%) and low-affinity sites, respectively. NMDA receptor subtypes expressed in Xenopus oocytes were blocked with IC50 values of 0.009 microM and 52 microM for the subunit combinations NR1C & NR2B and NR1C & NR2A, respectively, which indicated a >5000-fold selectivity. Like ifenprodil, Ro 25-6981 blocked NMDA receptor subtypes in an activity-dependent manner. Ro 25-6981 protected cultured cortical neurons against glutamate toxicity (16 h exposure to 300 microM glutamate) and combined oxygen and glucose deprivation (60 min followed by 20 h recovery) with IC50 values of 0.4 microM and 0.04 microM, respectively. Ro 25-6981 was more potent than ifenprodil in all of these tests. It showed no protection against kainate toxicity (exposure to 500 microM for 20 h) and only weak activity in blocking Na+ and Ca++ channels, activated by exposure of cortical neurons to veratridine (10 microM) and potassium (50 mM), respectively. These findings demonstrate that Ro 25-6981 is a highly selective, activity-dependent blocker of NMDA receptors that contain the NR2B subunit.
474 citations
TL;DR: Under conditions favoring reverse operation of the Na+–Ca2+ exchanger, Zn2+ application induced a slow increase in neurons and outward whole-cell current sensitive to benzamil–amiloride, suggesting that a second route of Zn 2+ entry into neurons may be via transporter-mediated exchange with intracellular Na+.
Abstract: We used the ratioable fluorescent dye mag-fura-5 to measure intracellular free Zn 2+ ([Zn 2+ ] i ) in cultured neocortical neurons exposed to neurotoxic concentrations of Zn 2+ in concert with depolarization or glutamate receptor activation and identified four routes of Zn 2+ entry. Neurons exposed to extracellular Zn 2+ plus high K + responded with a peak cell body signal corresponding to a [Zn 2+ ] i of 35–45 nm. This increase in [Zn 2+ ] i was attenuated by concurrent addition of Gd 3+ , verapamil, ω-conotoxin GVIA, or nimodipine, consistent with Zn 2+ entry through voltage-gated Ca 2+ channels. Furthermore, under conditions favoring reverse operation of the Na + –Ca 2+ exchanger, Zn 2+ application induced a slow increase in [Zn 2+ ] i and outward whole-cell current sensitive to benzamil–amiloride. Thus, a second route of Zn 2+ entry into neurons may be via transporter-mediated exchange with intracellular Na + . Both NMDA and kainate also induced rapid increases in neuronal [Zn 2+ ] i . The NMDA-induced increase was only partly sensitive to Gd 3+ or to removal of extracellular Na + , consistent with a third route of entry directly through NMDA receptor-gated channels. The kainate-induced increase was highly sensitive to Gd 3+ or Na + removal in most neurons but insensitive in a minority subpopulation (“cobalt-positive cells”), suggesting that a fourth route of neuronal Zn 2+ entry is through the Ca 2+ -permeable channels gated by certain subtypes of AMPA or kainate receptors.
451 citations
TL;DR: It is demonstrated that high-frequency stimulation of mossy fibres in rat hippocampal slices, in the presence of the highly selective AMPA receptor antagonist GYKI 53655, plus NMDA- and GABA-receptor antagonists, activates an inward current in CA3 neurons that has a pharmacology typical of kainate receptors.
Abstract: L-Glutamate, the principal excitatory neurotransmitter in the vertebrate central nervous system, acts on three classes of ionotropic glutamate receptors, named after the agonists AMPA, NMDA and kainate. AMPA receptors are known to mediate fast synaptic responses and NMDA receptors to mediate slow synaptic responses at most excitatory synapses in the brain. Kainate receptors are formed from a separate set of genes (GluR5-7, KA-1 and KA-2) and are widely distributed throughout the brain. They are implicated in epileptogenesis and cell death. However, the physiological functions of kainate receptors are not known. The development of 2,3-benzodiazepine antagonists that are selective for AMPA receptors enables kainate receptors to be specifically activated by exogenous ligands, such as kainate. Here we demonstrate that high-frequency stimulation of mossy fibres in rat hippocampal slices, in the presence of the highly selective AMPA receptor antagonist GYKI 53655 plus NMDA- and GABA-receptor antagonists, activates an inward current in CA3 neurons that has a pharmacology typical of kainate receptors. The finding that kainate receptors can be activated synaptically adds to the diversity of information transfer at glutamatergic synapses.
TL;DR: The effects of a potent and selective agonist and a selective antagonist are used to show that kainate receptors, comprised of or containing GluR5 subunits, regulate synaptic inhibition in the hippocampus, an action that could contribute to the epileptogenic effects of kainates.
Abstract: The principal excitatory neurotransmitter in the vertebrate central nervous system, L-glutamate, acts on three classes of ionotripic glutamate receptors, named after the agonists AMPA (α-amino-3-hydroxy-5-methyl-4-isoxalole-4-propionic acid), NMDA ( N -methyl-D-aspartate) and kainate1 The development of selective pharmacological agents has led to a detailed understanding ofthe physiological and pathological roles of AMPA and NMDA receptors2,3,4,5,6,7,8 In contrast, the lack of selective kainate receptor ligands has greatly hindered progress in understanding the rolesof kainate receptors9,10 Here we describe the effects of a potent and selective agonist, ATPA (( RS)-2-amino-3-(3-hydroxy-5- tert -butylisoxazol-4-yl)propanoic acid) and a selective antagonist, LY294486 ((3SR, 4aRS, 6SR, 8aRS)-6-((((1H-tetrazol-5-yl) methyl)oxy)methyl)-1, 2, 3, 4, 4a, 5, 6, 7, 8, 8a-decahydroisoquinoline-3-carboxylic acid), of the GluR5 subtype of kainate receptor11 We have used these agents to show that kainate receptors, comprised of or containing GluR5 subunits, regulate synaptic inhibition in the hippocampus, an action that could contribute to the epileptogenic effects of kainate12,13,14,15,16,17
TL;DR: It is found that increasing local levels of GABA by administration of a selective GABA-transaminase inhibitor, γ-vinyl-GABA, elicited robust feeding in satiated rats, suggesting a physiological role for endogenous AcbSh GABA in the control of feeding.
Abstract: We have demonstrated previously that injections of 6, 7-dinitroquinoxaline-2,3-dione into the nucleus accumbens shell (AcbSh) elicits pronounced feeding in satiated rats. This glutamate antagonist blocks AMPA and kainate receptors and most likely increases food intake by disrupting a tonic excitatory input to the AcbSh, thus decreasing the firing rate of a population of local neurons. Because the application of GABA agonists also decreases neuronal activity, we hypothesized that administration of GABA agonists into the AcbSh would stimulate feeding in satiated rats. We found that acute inhibition of cells in the AcbSh via administration of the GABAA receptor agonist muscimol or the GABAB receptor agonist baclofen elicited intense, dose-related feeding without altering water intake. Muscimol-induced feeding was blocked by coadministration of the selective GABAA receptor blocker bicuculline, but not by the GABAB receptor blocker saclofen. Conversely, baclofen-induced feeding was blocked by coadministration of saclofen, but was not affected by bicuculline. Furthermore, we found that increasing local levels of GABA by administration of a selective GABA-transaminase inhibitor, gamma-vinyl-GABA, elicited robust feeding in satiated rats, suggesting a physiological role for endogenous AcbSh GABA in the control of feeding. A mapping study showed that although some feeding can be elicited by muscimol injections near the lateral ventricles, the ventromedial AcbSh is the most sensitive site for eliciting feeding. These findings demonstrate that manipulation of GABA-sensitive cells in the AcbSh can have a pronounced, but specific, effect on feeding behavior in rats. They also constitute the initial description of a novel and potentially important component of the central mechanisms controlling food intake.
TL;DR: It is suggested that excessive activation of the ionotropic glutamate receptors expressed by oligodendrocytes may act as a negative regulator of the size of this cell population.
Abstract: In cultured oligodendrocytes isolated from perinatal rat optic nerves, we have analyzed the expression of ionotropic glutamate receptor subunits as well as the effect of the activation of these receptors on oligodendrocyte viability. Reverse transcription–PCR, in combination with immunocytochemistry, demonstrated that most oligodendrocytes differentiated in vitro express the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits GluR3 and GluR4 and the kainate receptor subunits GluR6, GluR7, KA1 and KA2. Acute and chronic exposure to kainate caused extensive oligodendrocyte death in culture. This effect was partially prevented by the AMPA receptor antagonist GYKI 52466 and was completely abolished by the non-N-methyl-d-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), suggesting that both AMPA and kainate receptors mediate the observed kainate toxicity. Furthermore, chronic application of kainate to optic nerves in vivo resulted in massive oligodendrocyte death which, as in vitro, could be prevented by coinfusion of the toxin with CNQX. These findings suggest that excessive activation of the ionotropic glutamate receptors expressed by oligodendrocytes may act as a negative regulator of the size of this cell population.
TL;DR: Results indicate that kainate receptor activation down-regulates GABAergic inhibition by modulating the reliability of GABA synapses and reducing the frequency of miniature IPSCs.
TL;DR: COX-2 is transiently induced after SD and focal ischemia by activation of N-methyl-D-aspartic acid-receptors and PLA2, most prominently in cortical neurons that are at a high risk to die after focal brain ischemIA.
Abstract: Repetitive spreading depression (SD) waves, involving depolarization of neurons and astrocytes and up-regulation of glucose consumption, is thought to lower the threshold of neuronal death during and immediately after ischemia. Using rat models for SD and focal ischemia we investigated the expression of cyclooxygenase-1 (COX-1), the constitutive form, and cyclooxygenase-2 (COX-2), the inducible form of a key enzyme in prostaglandin biosynthesis and the target enzymes for nonsteroidal anti-inflammatory drugs. Whereas COX-1 mRNA levels were undetectable and uninducible, COX-2 mRNA and protein levels were rapidly increased in the cortex, especially in layers 2 and 3 after SD and transient focal ischemia. The cortical induction was reduced by MK-801, an N-methyl-d-aspartic acid-receptor antagonist, and by dexamethasone and quinacrine, phospholipase A2 (PLA2) inhibiting compounds. MK-801 acted by blocking SD whereas treatment with PLA2 inhibitors preserved the wave propagation. NBQX, an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-receptor antagonist, did not affect the SD-induced COX-2 expression, whereas COX-inhibitors indomethacin and diclofenac, as well as a NO synthase-inhibitor, NG-nitro-l-arginine methyl ester, tended to enhance the COX-2 mRNA expression. In addition, ischemia induced COX-2 expression in the hippocampal and perifocal striatal neurons and in endothelial cells. Thus, COX-2 is transiently induced after SD and focal ischemia by activation of N-methyl-d-aspartic acid-receptors and PLA2, most prominently in cortical neurons that are at a high risk to die after focal brain ischemia.
TL;DR: The present data suggest that the δ2 receptors are targeted selectively to a subset of Purkinje cell spines and that they are coexpressed with ionotropic receptors in the postsynaptic specialization.
Abstract: The δ2 glutamate receptors are prominently expressed in Purkinje cells and are thought to play a key role in the induction of cerebellar long-term depression The synaptic and subsynaptic localization of δ receptors in rat cerebellar cortex was investigated with sensitive and high-resolution immunogold procedures After postembedding incubation with an antibody raised to a C-terminal peptide of δ2, high gold particle densities occurred in all parallel fiber synapses with Purkinje cell dendritic spines, whereas other synapses were consistently devoid of labeling Among the types of immunonegative synapse were climbing fiber synapses with spines and parallel fiber synapses with dendritic stems of interneurons At the parallel fiber–spine synapse, gold particles signaling δ receptors were restricted to the postsynaptic specialization By the use of double labeling with two different gold particle sizes, it was shown that δ and AMPA GluR2/3 receptors were colocalized along the entire extent of the postsynaptic specialization without forming separate domains The distribution of gold particles representing δ receptors was consistent with a cytoplasmic localization of the C terminus and an absence of a significant presynaptic pool of receptor molecules The present data suggest that the δ2 receptors are targeted selectively to a subset of Purkinje cell spines and that they are coexpressed with ionotropic receptors in the postsynaptic specialization This arrangement could allow for a direct interaction between the two classes of receptor
TL;DR: The results indicate that neuregulins regulate the composition of neurotransmitter receptors in maturing synapses in the brain, in a manner analogous to the neuromuscular junction.
Abstract: Neuregulins (also known as ARIA, NDF, heregulin, GGF) are a family of widely expressed growth and differentiation factors Neuregulins secreted from motor neurons accumulate at maturing neuromuscular junctions, where they stimulate transcription of genes encoding specific acetylcholine receptors How these factors function at central synapses, however, is unknown In the maturing cerebellum, neuregulins are concentrated in glutamatergic mossy fibres that innervate granule cells in the internal granule-cell layer1 We have analysed the effects of neuregulins on the expression of genes encoding NMDA (N-methyl-D-aspartate) receptors in the cerebellum, because receptor composition changes dramatically as expression of the receptor NR2C subunit is specifically induced in neurons in the internal granule-cell layer during synaptogenesis Here we report that addition of a neuregulin-β isoform to cultured cerebellar slices specifically increases the expression of NR2C messenger RNAs by at least 100-fold; effects are only minor with a neuregulin-α isoform This stimulation of NR2C expression requires synaptic activity by NMDA receptors, as well as neuregulin-β Addition of the NMDA-receptor-channel blocker AP-5 prevents upregulation of the NR2C subunit by neuregulin, whereas an AMPA/kainate-receptor antagonist does not Consistent with these effects of neuregulin, we find that granule cells express its receptors ErbB2 and ErbB4 before the NR2C subunit of the NMDA receptor Our results indicate that neuregulins regulate the composition of neurotransmitter receptors in maturing synapses in the brain, in a manner analogous to the neuromuscular junction
TL;DR: It is suggested that availability of ammonia and energy demands are major factors determining the metabolic fate of glutamate in astrocytes.
Abstract: Glutamate uptake and metabolism was studied in cerebral cortical astrocytes The expression of the astrocytic glutamate transporter GLAST was found to be stimulated by extracellular glutamate through activation of kainate receptors on the astrocytes Energy metabolism and ammonia homeostasis are two important aspects of glutamate handling in astrocytes It is well known that glutamate transport into astrocytes and glutamine formation are energy consuming processes Furthermore, ammonia is required for glutamine production On the other hand, glutamate metabolism through the tricarboxylic acid cycle is an energy and ammonia producing pathway In the present study it was shown that at an extracellular glutamate concentration of 05 mM, high energy phosphates were reduced, and more than 50% of the glutamate carbon skeleton entered the tricarboxylic acid cycle to yield products like lactate, aspartate, and additionally glutamate and glutamine derived from tricarboxylic acid cycle intermediates Entry into the cycle was not affected by the transaminase inhibitor aminooxyacetic acid, indicating that deamination is the major route for 2-oxoglutarate formation from glutamate Synthesis of glutamate from 2-oxoglutarate, however, proceeded via transamination In an earlier study it was shown that at glutamate concentrations at and below 02 mM, glutamine appears to be the major product and entry of glutamate into the tricarboxylic acid cycle is decreased 70% by aminooxyacetic acid In an attempt to unify the above mentioned results, it is suggested that availability of ammonia and energy demands are major factors determining the metabolic fate of glutamate in astrocytes
TL;DR: In K+ channels and glutamate receptors, some of the amino acids in the receptor/channel structure that influence to polyamines have been identified, leading to a partial understanding of the effects of polyamines at a molecular level.
TL;DR: In summary, non-NMDA ionotropic glutamate receptors seem to be involved in the pathophysiology of traumatic spinal cord injury.
Abstract: We examined the role of glutamatergic mechanisms in acute injury to rat spinal cord white matter. Compound action potentials (CAPs) were recorded from isolated dorsal column segments in vitro . Under control conditions (Ringer’s solution), the CAPs decreased to 71.4 ± 2.0% of preinjury values after compression injury with a clip exerting a closing force of 2 g . The combination of the NMDA receptor blocker APV (50 μm) and the AMPA/kainate (KA) receptor blocker CNQX (10 μm) resulted in significantly improved recovery of CAP amplitude postinjury; however, the NMDA receptor antagonist APV alone did not enhance postinjury recovery, and infusion of NMDA (10 μm) did not affect recovery of the CAPs. In contrast, the AMPA/KA receptor blockers NBQX (10 μm) or CNQX (10 μm) significantly enhanced the recovery of CAP amplitude postinjury. The agonists AMPA (100 μm) or KA (100 μm) resulted in significant attenuation of CAP amplitude postinjury. Coapplication of AMPA/KA plus NBQX and CNQX was also associated with improved functional recovery. After incubation with AMPA and KA, Co2+-positive glia were visualized in spinal cord white matter. Similar results were seen after compressive injury but not in control cords. Immunohistochemistry and Western blot analysis demonstrated AMPA (GluR4)- and KA (GluR6/7 and KA2)-positive astrocytes in spinal cord white matter. In summary, non-NMDA ionotropic glutamate receptors seem to be involved in the pathophysiology of traumatic spinal cord injury. The presence of AMPA (GluR4) and KA (GluR6/7 and KA2) receptors on periaxonal astrocytes suggests a role for these cells in glutamatergic white matter injury.
TL;DR: Results demonstrate that glutamate receptors are targeted to specific postsynaptic populations of glutamatergic synapses.
TL;DR: Understanding of the structure-function relationship of one aspect of pharmacology common to both insect and vertebrate GABA receptors, namely antagonism by the plant-derived toxin picrotoxinin is enhanced.
TL;DR: The results begin to characterize the events regulating the distribution of AMPA receptors and demonstrate similarities between synapse formation at the neuromuscular junction and at excitatory synapses in cultured neurons.
Abstract: Although the regulation of neurotransmitter receptors during synaptogenesis has been studied extensively at the neuromuscular junction, little is known about the control of excitatory neurotransmitter receptors during synapse formation in central neurons. Using antibodies against extracellular N-terminal (N-GluR1) and intracellular C-terminal (C-GluR1) domains of the AMPA receptor subunit GluR1, combined with surface biotinylation and metabolic labeling studies, we have characterized the redistribution and metabolic stabilization of the AMPA receptor subunit GluR1 during synapse formation in culture. Before synapse formation, GluR1 is distributed widely, both on the surface and within the dendritic cytoplasm of these neurons. The diffuse cell surface pool of receptor appears to be mobile within the membrane and can be induced to cluster by the addition of N-GluR1 to live neurons. As cultures mature and synapses form, there is a redistribution of surface GluR1 into clusters at excitatory synapses where it appears to be immobilized. The change in the distribution of GluR1 is accompanied by an increase in both the half-life of the receptor and the percentage of the total pool of GluR1 that is present on the cell surface. Blockade of postsynaptic AMPA and NMDA receptors had no effect on the redistribution of GluR1. These results begin to characterize the events regulating the distribution of AMPA receptors and demonstrate similarities between synapse formation at the neuromuscular junction and at excitatory synapses in cultured neurons.
TL;DR: It is suggested that the spontaneous discharge of DA cells is inhibited in the dark by GABAergic amacrines that receive their input from off-bipolars.
TL;DR: In this paper, the composition of AMPA receptors expressed on normal human spinal motor neurons by in situ hybridization was investigated to determine their likely subunit stoichiometry, and significant levels of mRNA were detected for the GluR1,GluR3, and GLuR4 subunits.
Abstract: The cause of the selective degeneration of motor neurons in amyotrophic lateral sclerosis (ALS) remains unexplained. One potential pathogenetic mechanism is chronic toxicity due to disturbances of the glutamatergic neurotransmitter system, mediated via alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-sensitive glutamate receptors. Functional AMPA receptors consist of various combinations of four subunits (designated GluR1-4). The GluR2 subunit is functionally dominant and renders AMPA receptors impermeable to calcium. Most native AMPA receptors in the mammalian central nervous system (CNS) contain the GluR2 subunit and are calcium impermeable. We have investigated the composition of AMPA receptors expressed on normal human spinal motor neurons by in situ hybridization to determine their likely subunit stoichiometry. Highly significant levels of mRNA were detected for the GluR1, GluR3, and GluR4 subunits. However, GluR2 subunit mRNA was not detectable in this cell group. The absence of detectable GluR2 mRNA in normal human spinal motor neurons predicts that they express calcium-permeable AMPA receptors unlike most neuronal groups in the human CNS. Expression of atypical calcium-permeable AMPA receptors by human motor neurons provides a possible mechanism whereby disturbances of glutamate neurotransmission in ALS may selectively injure this cell group.
TL;DR: It is reported here that the GluR7 subunit and a novel carboxy-terminal splice variant, GLUR7b, are functional glutamate receptors with unique pharmacological properties and glutamate exhibits a 10-fold lower potency for (non-desensitized) Glu R7-mediated currents as compared to other non-NMDA receptor channels.
TL;DR: It is hypothesized that peripheral glutamate receptors on cutaneous axons can be manipulated to reduce certain aspects of pain of peripheral origin and this route of administration offers the advantage of avoiding the side effects of systemic administration.
Abstract: The present study demonstrates that local cutaneous administration of either the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist MK-801 or the non-NMDA glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) significantly attenuates formalin-induced nociceptive behaviors. Specifically, pretreatment with either drug reduced the magnitude and time course of lifting and licking behavior in the late phase of formalin pain; however, flinching behavior was not affected. In contrast, post-treatment of formalin pain with either antagonist did not affect lifting and licking behavior, although flinching behavior was mildly attenuated. We hypothesize that these actions result from blocking of peripheral glutamate receptors located on unmyelinated axons at the dermal-epidermal junction. These data suggest that peripheral glutamate receptors on cutaneous axons can be manipulated to reduce certain aspects of pain of peripheral origin. This route of administration offers the advantage of avoiding the side effects of systemic administration.
TL;DR: A large fraction of the current induced by parallel fibre stimulation reflects the uptake of synaptically released glutamate, consistent with the effect of this anion on glutamate transporters.
Abstract: 1. Whole-cell recordings were obtained from Bergmann glial cells in rat cerebellar slices. 2. The cells had low input resistances (70 +/- 38 M omega; n = 13) and a mean resting potential of -82 +/- 6 mV (n = 12) with a potassium-based internal solution. Electrical and dye coupling between Bergmann glia were confirmed. 3. Stimulation of parallel fibres induced a complex, mostly inward current which could be decomposed pharmacologically. 4. The ionotropic glutamate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM), but not DL-2-amino-5-phosphonopentanoic acid (DL-APV; 100 microM) consistently blocked an early inward current component that may reflect synaptic activation of AMPA/kainate receptors in Bergmann glia. 5. Addition of cadmium ions (100 microM) to inhibit transmitter release blocked most of the CNQX-APV-insensitive current. This component probably reflects electrogenic uptake of the synaptically released glutamate. 6. Tetrodotoxin (TTX; 1 microM) blocked the remaining inward current: a slow component, possibly produced by the potassium ion efflux during action potential propagation in parallel fibres. An initial triphasic component of the response was also TTX sensitive and reflected passage of the parallel fibre action potential volley. 7. The putative glutamate uptake current was further characterized; it was blocked by the competitive uptake blockers D-aspartate (0.5 mM) and L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC; 0.5 mM), and by replacement of sodium with lithium. Monitoring the triphasic TTX-sensitive component showed that this inhibition did not result from changes of action potential excitation and propagation. 8. Intracellular nitrate ions increased the putative uptake current, consistent with the effect of this anion on glutamate transporters. 9. The putative uptake current was reduced by depolarization, consistent with the voltage dependence of glutamate uptake. 10. It is concluded that a large fraction of the current induced by parallel fibre stimulation reflects the uptake of synaptically released glutamate. The uptake current activated rapidly, with a 20-80% rise time of 2.3 +/- 0.7 ms (n = 10), and decayed with a principal time constant of 25 +/- 6 ms (n = 10).
TL;DR: A polyclonal antibody was produced to a 16 amino acid peptide near the C-terminus of GluR2 and was affinity-purified in a three-step procedure.
Abstract: Alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors are the major excitatory neurotransmitter receptors of the central nervous system. AMPA receptor complexes that contain the AMPA-type glutamate receptor subunit 2 (GluR2) are responsible for the low calcium permeability typical of most AMPA receptors, and the absence of GluR2 may be a key factor in neurotoxicity. A polyclonal antibody was produced to a 16 amino acid peptide near the C-terminus of GluR2 and was affinity-purified in a three-step procedure. The antibody did not recognize other AMPA subunits in transfected cells with the use of either Western blots or immunocytochemistry. This highly specific GluR2 antibody was used to provide a specific morphological study of GluR2 protein distribution in neurons and synapses of the rat. GluR2 is prevalent in most principal neurons throughout the telencephalon. Neurons with few or no GluR2 subunits include two major types: 1) some populations of interneurons of the telencephalon and of some other areas and 2) many populations of principal neurons in the brainstem and spinal cord. Immunofluorescence showed that GluR2 immunolabeling was widespread, including in dendrites and puncta, in the hippocampus and neocortex. Where they were present, GluR2 subunits colocalized with other AMPA receptor subunits in individual neurons. Electron microscopy of the hippocampus showed GluR2-bearing, calcium-impermeable AMPA receptors postsynaptic to dendrite synapses of forebrain principal neurons. In addition, electron microscopy of the neocortex showed significant staining in postsynaptic profiles. Electron microscopy of the cerebellum revealed the presence of GluR2 subunits in the postsynaptic profiles of many parallel fiber/Purkinje cell spine synapses, whereas electron microscopy of the spinal cord showed substantial staining in the postsynaptic profiles of dorsal horn synapses, but not in ventral horn synapses. Both ultrastructural and immunofluorescence data showed that calcium-impermeable AMPA receptors are widespread in dendrite arborizations.