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Blakemore LJ, Trombley PQ. Zinc Modulates Olfactory Bulb Kainate Receptors. Neuroscience 2020; 428:252-268. [PMID: 31874243 PMCID: PMC7193548 DOI: 10.1016/j.neuroscience.2019.11.041] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2019] [Revised: 11/22/2019] [Accepted: 11/26/2019] [Indexed: 10/25/2022]
Abstract
Kainate receptors (KARs) are glutamate receptors with ionotropic and metabotropic activity composed of the GluK1-GluK5 subunits. We previously reported that KARs modulate excitatory and inhibitory transmission in the olfactory bulb (OB). Zinc, which is highly concentrated in the OB, also appears to modulate OB synaptic transmission via actions at other ionotropic glutamate receptors (i.e., AMPA, NMDA). However, few reports of effects of zinc on recombinant and/or native KARs exist and none have involved the OB. In the present study, we investigated the effects of exogenously applied zinc on OB KARs expressed by mitral/tufted (M/T) cells. We found that 100 µM zinc inhibits currents evoked by various combinations of KAR agonists (kainate or SYM 2081) and the AMPA receptor antagonist SYM 2206. The greatest degree of zinc-mediated inhibition was observed with coapplication of zinc with the GluK1- and GluK2-preferring agonist SYM 2081 plus SYM 2206. This finding is consistent with prior reports of zinc's inhibitory effects on some recombinant (homomeric GluK1 and GluK2 and heteromeric GluK2/GluK4 and GluK2/GluK5) KARs, although potentiation of other (GluK3, GluK2/3) KARs has also been described. It is also of potential importance given our previously reported molecular data suggesting that OB neurons express relatively high levels of GluK1 and GluK2. Our present findings suggest that a physiologically relevant concentration of zinc modulates KARs expressed by M/T cells. As M/T cells are targets of zinc-containing olfactory sensory neurons, synaptically released zinc may influence odor information-encoding synaptic circuits in the OB via actions at KARs.
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Affiliation(s)
- Laura J Blakemore
- Program in Neuroscience, Florida State University, Tallahassee, FL, USA; Department of Biological Science, Florida State University, Tallahassee, FL, USA
| | - Paul Q Trombley
- Program in Neuroscience, Florida State University, Tallahassee, FL, USA; Department of Biological Science, Florida State University, Tallahassee, FL, USA.
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Blakemore LJ, Corthell JT, Trombley PQ. Kainate Receptors Play a Role in Modulating Synaptic Transmission in the Olfactory Bulb. Neuroscience 2018; 391:25-49. [PMID: 30213766 DOI: 10.1016/j.neuroscience.2018.09.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Revised: 08/31/2018] [Accepted: 09/03/2018] [Indexed: 02/06/2023]
Abstract
Glutamate is the neurotransmitter used at most excitatory synapses in the mammalian brain, including those in the olfactory bulb (OB). There, ionotropic glutamate receptors including N-methyl-d-aspartate receptors (NMDARs) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) play a role in processes such as reciprocal inhibition and glomerular synchronization. Kainate receptors (KARs) represent another type of ionotropic glutamate receptor, which are composed of five (GluK1-GluK5) subunits. Whereas KARs appear to be heterogeneously expressed in the OB, evidence as to whether these KARs are functional, found at synapses, or modify synaptic transmission is limited. In the present study, coapplication of KAR agonists (kainate, SYM 2081) and AMPAR antagonists (GYKI 52466, SYM 2206) demonstrated that functional KARs are expressed by OB neurons, with a subset of receptors located at synapses. Application of kainate and the GluK1-selective agonist ATPA had modulatory effects on excitatory postsynaptic currents (EPSCs) evoked by stimulation of the olfactory nerve layer. Application of kainate and ATPA also had modulatory effects on reciprocal inhibitory postsynaptic currents (IPSCs) evoked using a protocol that evokes dendrodendritic inhibition. The latter finding suggests that KARs, with relatively slow kinetics, may play a role in circuits in which the relatively brief duration of AMPAR-mediated currents limits the role of AMPARs in synaptic transmission (e.g., reciprocal inhibition at dendrodendritic synapses). Collectively, our findings suggest that KARs, including those containing the GluK1 subunit, modulate excitatory and inhibitory transmission in the OB. These data further suggest that KARs participate in the regulation of synaptic circuits that encode odor information.
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Affiliation(s)
- Laura J Blakemore
- Program in Neuroscience, Florida State University, Tallahassee, FL, United States; Department of Biological Science, Florida State University, Tallahassee, FL, United States
| | - John T Corthell
- Program in Neuroscience, Florida State University, Tallahassee, FL, United States; Department of Biological Science, Florida State University, Tallahassee, FL, United States
| | - Paul Q Trombley
- Program in Neuroscience, Florida State University, Tallahassee, FL, United States; Department of Biological Science, Florida State University, Tallahassee, FL, United States.
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Alcaide A, Marconi L, Marek A, Haym I, Nielsen B, Møllerud S, Jensen M, Conti P, Pickering DS, Bunch L. Synthesis and pharmacological characterization of the selective GluK1 radioligand (S)-2-amino-3-(6-[3H]-2,4-dioxo-3,4-dihydrothieno[3,2-d]pyrimidin-1(2H)-yl)propanoic acid ([3H]-NF608). MEDCHEMCOMM 2016. [DOI: 10.1039/c6md00339g] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Expedite synthesis of [3H]NF608 – a new subtype selective GluK1 radioligand.
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Affiliation(s)
- Anna Alcaide
- Department of Drug Design and Pharmacology
- Faculty of Health and Medical Sciences
- University of Copenhagen
- Denmark
| | - Laura Marconi
- Department of Drug Design and Pharmacology
- Faculty of Health and Medical Sciences
- University of Copenhagen
- Denmark
- Dipartimento di Scienze Farmaceutiche
| | - Ales Marek
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences
- Prague 6
- Czech Republic
| | - Isabell Haym
- Department of Drug Design and Pharmacology
- Faculty of Health and Medical Sciences
- University of Copenhagen
- Denmark
| | - Birgitte Nielsen
- Department of Drug Design and Pharmacology
- Faculty of Health and Medical Sciences
- University of Copenhagen
- Denmark
| | - Stine Møllerud
- Department of Drug Design and Pharmacology
- Faculty of Health and Medical Sciences
- University of Copenhagen
- Denmark
| | - Mikael Jensen
- Nutech Hevesy Laboratory
- The Technical University of Denmark
- Denmark
| | - Paola Conti
- Dipartimento di Scienze Farmaceutiche
- Università degli Studi di Milano
- 20133 Milano
- Italy
| | - Darryl S. Pickering
- Department of Drug Design and Pharmacology
- Faculty of Health and Medical Sciences
- University of Copenhagen
- Denmark
| | - Lennart Bunch
- Department of Drug Design and Pharmacology
- Faculty of Health and Medical Sciences
- University of Copenhagen
- Denmark
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Kainate receptors mediate synaptic input to transient and sustained OFF visual pathways in primate retina. J Neurosci 2014; 34:7611-21. [PMID: 24872565 DOI: 10.1523/jneurosci.4855-13.2014] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Visual signals are segregated into parallel pathways at the first synapse in the retina between cones and bipolar cells. Within the OFF pathways of mammals, the selective expression of AMPA or kainate-type glutamate receptors in the dendrites of different OFF-bipolar cell types is thought to contribute to formation of distinct temporal channels. AMPA receptors, with rapid recovery from desensitization, are proposed to transmit high temporal frequency signals, whereas kainate receptors (KARs) are presumed to encode lower temporal frequencies. Here we studied the glutamate receptors expressed by OFF-bipolar cells in slice preparations of macaque monkey retina, where the low (midget/parvocellular) and high-frequency (parasol/magnocellular) temporal channels are well characterized. We found that all OFF-bipolar types receive input primarily through KARs and that KAR antagonists block light-evoked input to both OFF-midget and OFF-parasol ganglion cells. KAR subunits were differentially expressed in OFF-bipolar types; the diffuse bipolar (DB) cells, DB2 and DB3b, expressed GluK1 and showed transient responses to glutamate and the KAR agonist, ATPA. In contrast, flat midget bipolar, DB1, and DB3a cells lacked GluK1 and showed relatively sustained responses. Finally, we found that the KAR accessory protein, Neto1, is expressed at the base of cone pedicles but is not colocalized with the GluK1 subunit. In summary, the results indicate that transient signaling in the OFF pathway of macaques is not dependent on AMPA receptors and that heterogeneity of KARs and accessory proteins may contribute to the formation of parallel temporal channels.
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Fritsch B, Reis J, Gasior M, Kaminski RM, Rogawski MA. Role of GluK1 kainate receptors in seizures, epileptic discharges, and epileptogenesis. J Neurosci 2014; 34:5765-75. [PMID: 24760837 PMCID: PMC3996208 DOI: 10.1523/jneurosci.5307-13.2014] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2013] [Revised: 02/12/2014] [Accepted: 03/07/2014] [Indexed: 11/21/2022] Open
Abstract
Kainate receptors containing the GluK1 subunit have an impact on excitatory and inhibitory neurotransmission in brain regions, such as the amygdala and hippocampus, which are relevant to seizures and epilepsy. Here we used 2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA), a potent and selective agonist of kainate receptors that include the GluK1 subunit, in conjunction with mice deficient in GluK1 and GluK2 kainate receptor subunits to assess the role of GluK1 kainate receptors in provoking seizures and in kindling epileptogenesis. We found that systemic ATPA, acting specifically via GluK1 kainate receptors, causes locomotor arrest and forelimb extension (a unique behavioral characteristic of GluK1 activation) and induces myoclonic behavioral seizures and electrographic seizure discharges in the BLA and hippocampus. In contrast, the proconvulsant activity of systemic AMPA, kainate, and pentylenetetrazol is not mediated by GluK1 kainate receptors, and deletion of these receptors does not elevate the threshold for seizures in the 6 Hz model. ATPA also specifically activates epileptiform discharges in BLA slices in vitro via GluK1 kainate receptors. Olfactory bulb kindling developed similarly in wild-type, GluK1, and GluK2 knock-out mice, demonstrating that GluK1 kainate receptors are not required for epileptogenesis or seizure expression in this model. We conclude that selective activation of kainate receptors containing the GluK1 subunit can trigger seizures, but these receptors are not necessary for seizure generation in models commonly used to identify therapeutic agents for the treatment of epilepsy.
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Affiliation(s)
- Brita Fritsch
- Epilepsy Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
- Department of Neurology, University Hospital, 79106 Freiburg, Germany, and
| | - Janine Reis
- Epilepsy Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
- Department of Neurology, University Hospital, 79106 Freiburg, Germany, and
| | - Maciej Gasior
- Epilepsy Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Rafal M. Kaminski
- Epilepsy Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Michael A. Rogawski
- Epilepsy Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
- Department of Neurology, School of Medicine and Center for Neuroscience, University of California, Davis, Sacramento, California 95817
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6
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Martinez-Perez JA, Iyengar S, Shannon HE, Bleakman D, Alt A, Clawson DK, Arnold BM, Bell MG, Bleisch TJ, Castaño AM, Del Prado M, Dominguez E, Escribano AM, Filla SA, Ho KH, Hudziak KJ, Jones CK, Mateo A, Mathes BM, Mattiuz EL, Ogden AML, Simmons RMA, Stack DR, Stratford RE, Winter MA, Wu Z, Ornstein PL. GluK1 antagonists from 6-(tetrazolyl)phenyl decahydroisoquinoline derivatives: In vitro profile and in vivo analgesic efficacy. Bioorg Med Chem Lett 2013; 23:6463-6. [DOI: 10.1016/j.bmcl.2013.09.045] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 09/13/2013] [Accepted: 09/13/2013] [Indexed: 11/15/2022]
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7
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Martinez-Perez JA, Iyengar S, Shannon HE, Bleakman D, Alt A, Arnold BM, Bell MG, Bleisch TJ, Castaño AM, Del Prado M, Dominguez E, Escribano AM, Filla SA, Ho KH, Hudziak KJ, Jones CK, Mateo A, Mathes BM, Mattiuz EL, Ogden AML, Simmons RMA, Stack DR, Stratford RE, Winter MA, Wu Z, Ornstein PL. GluK1 antagonists from 6-(carboxy)phenyl decahydroisoquinoline derivatives. SAR and evaluation of a prodrug strategy for oral efficacy in pain models. Bioorg Med Chem Lett 2013; 23:6459-62. [DOI: 10.1016/j.bmcl.2013.09.046] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2013] [Revised: 09/13/2013] [Accepted: 09/13/2013] [Indexed: 11/25/2022]
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8
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Lv Q, Liu Y, Han D, Xu J, Zong YY, Wang Y, Zhang GY. Neuroprotection of GluK1 kainate receptor agonist ATPA against ischemic neuronal injury through inhibiting GluK2 kainate receptor-JNK3 pathway via GABA(A) receptors. Brain Res 2012; 1456:1-13. [PMID: 22516108 DOI: 10.1016/j.brainres.2012.03.050] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Revised: 03/19/2012] [Accepted: 03/21/2012] [Indexed: 12/21/2022]
Abstract
It is well known that GluK2-containing kainate receptors play essential roles in seizure and cerebral ischemia-induced neuronal death, while GluK1-containing kainate receptors could increase tonic inhibition of post-synaptic pyramidal neurons. This research investigated whether GluK1 could inhibit activation of c-Jun N-terminal kinase 3 (JNK3) signaling pathway mediated by the GluK2 in cerebral ischemia-reperfusion. The results show that GluK1 activation by (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA) at 1nmol per rat could inhibit the assembly of GluK2·Postsynaptic density 95·mixed lineage kinase 3 signaling module, activation of JNK3 and its downstream signal molecules. However, the inhibition of ATPA could be prevented by GluK1 antagonist NS3763, GluK1 antisense, and GABA(A) receptor antagonist bicuculline. In addition, ATPA played a neuroprotective role against cerebral ischemia. In sum, the findings indicate that activation of GluK1 by ATPA at specific dosages may promote GABA release, which then suppresses post-synaptic GluK2-JNK3 signaling-mediated cerebral ischemic injury via GABA(A)R.
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Affiliation(s)
- Qian Lv
- Research Center for Biochemistry and Molecular Biology, Jiangsu Key Laboratory of Brain Disease Bio-information, Xuzhou Medical College, Xuzhou 221002, Jiangsu, PR China
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9
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Duncan GE, Koller BH, Moy SS. Effects of the selective kainate receptor antagonist ACET on altered sensorimotor gating in a genetic model of reduced NMDA receptor function. Brain Res 2012; 1443:98-105. [PMID: 22297176 DOI: 10.1016/j.brainres.2012.01.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 01/06/2012] [Accepted: 01/06/2012] [Indexed: 12/19/2022]
Abstract
The pathophysiology of schizophrenia may involve reduced NMDA receptor function. Accordingly, experimental models of NMDA receptor hypofunction may be useful for testing potential new antipsychotic agents and for characterizing neurobiological abnormalities relevant to schizophrenia. We demonstrated previously that mice under-expressing the NR1 subunit of the NMDA receptor show supersensitive behavioral responses to kainic acid and that a kainate receptor antagonist normalized altered behaviors in the mutant mice (NR1(neo/neo)). The present work examined effects of another selective kainate receptor antagonist, (S)-1-(2-Amino-2-carboxyethyl)-3-(2-carboxy-5-phenylthiophene-3-yl-methylpyrimidine-2,4-dione (ACET), on altered behavioral phenotypes in the genetic model of NMDA receptor hypofunction. ACET, at a dose of 15 mg/kg, partially reversed the deficits in prepulse inhibition produced by the mutation. The 15 mg/kg dose of ACET was also effective in reversing behavioral effects of the selective kainate agonist ATPA. However, ACET did not significantly reduce the increased locomotor activity and rearing behavior observed in the NR1(neo/neo) mice. These findings show that a highly selective kainate receptor antagonist can affect the deficits in sensorimotor gating in the NR1(neo/neo) mice. The results also provide further support for the idea that selective kainate receptor antagonists could be novel therapeutic candidates for schizophrenia.
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Affiliation(s)
- Gary E Duncan
- Department of Psychiatry, University of North Carolina at Chapel Hill, NC 27599, USA.
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10
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Munasinghe JP, Banerjee M, Acosta MT, Banks M, Heffer A, Silva AC, Koretsky A, Theodore WH. Arterial spin labeling demonstrates that focal amygdalar glutamatergic agonist infusion leads to rapid diffuse cerebral activation. Acta Neurol Scand 2010; 121:209-16. [PMID: 19951270 DOI: 10.1111/j.1600-0404.2009.01188.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
OBJECTIVES To investigate acute effects of intra-amygdalar excitatory amino acid administration on blood flow, relaxation time and apparent diffusion coefficient in rat brain. MATERIALS AND METHODS Several days after MR-compatible cannula placement in right basolateral amygdala, anesthetized rats were imaged at 7 T. Relative cerebral blood flow (CBF) was measured before and 60 min after infusion of 10 nmol KA, cAMPA, ATPA, or normal saline using arterial spin labeling. Quantitative T(2) and diffusion-weighted images were acquired. rCBF, T(2) and ADC values were evaluated in bilateral basolateral amygdala, hippocampus, basal ganglia, frontal and parietal regions. RESULTS KA led to the highest, and ATPA lowest bilateral rCBF increases. Time courses varied among drugs. T(2) for KA and AMPA was higher while ADC was lower for KA. CONCLUSIONS Intra-amygdalar injection of GluR agonists evoked bilateral seizure activity and increased rCBF, greater for KA and AMPA than selective ATPA GluR5 activation.
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Affiliation(s)
- J P Munasinghe
- MRI Research Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA
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11
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Platel JC, Heintz T, Young S, Gordon V, Bordey A. Tonic activation of GLUK5 kainate receptors decreases neuroblast migration in whole-mounts of the subventricular zone. J Physiol 2008; 586:3783-93. [PMID: 18565997 DOI: 10.1113/jphysiol.2008.155879] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In the postnatal subventricular zone (SVZ), neuroblasts migrate in chains along the lateral ventricle towards the olfactory bulb. AMPA/kainate receptors as well as metabotropic glutamate receptors subtype 5 (mGluR5) are expressed in SVZ cells. However, the cells expressing these receptors and the function of these receptors remain unexplored. We thus examined whether SVZ neuroblasts express mGluR5 and Ca(2+)-permeable kainate receptors in mouse slices. Doublecortin (DCX)-immunopositive cells (i.e. neuroblasts) immunostained positive for mGluR5 and GLU(K5-7)-containing kainate receptors. RT-PCR from approximately 10 GFP-fluorescent cell aspirates obtained in acute slices from transgenic mice expressing green fluorescent protein (GFP) under the DCX promoter showed mGluR5 and GLU(K5) receptor mRNA in SVZ neuroblasts. Patch-clamp data suggest that approximately 60% of neuroblasts express functional GLU(K5)-containing receptors. Activation of mGluR5 and GLU(K5)-containing receptors induced Ca(2+) increases in 50% and 60% of SVZ neuroblasts, respectively, while most neuroblasts displayed GABA(A)-mediated Ca(2+) responses. To examine the effects of these receptors on the speed of neuroblast migration, we developed a whole-mount preparation of the entire lateral ventricle from postnatal day (P) 20-25 DCX-GFP mice. The GABA(A) receptor (GABA(A)R) antagonist bicuculline increased the speed of neuroblast migration by 27%, as previously reported in acute slices. While the mGluR5 antagonist MPEP did not affect the speed of neuroblast migration, the homomeric and heteromeric GLU(K5) receptor antagonists, NS3763 and UB302, respectively, increased the migration speed by 38%. These data show that although both GLU(K5) receptor and mGluR5 activations increase Ca(2+) in neuroblasts, only GLU(K5) receptors tonically reduce the speed of neuroblast migration along the lateral ventricle.
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Affiliation(s)
- Jean-Claude Platel
- Department of Neurosurgery, Yale University School of Medicine, 333 Cedar Street, FMB 422, New Haven, CT 06520-8082, USA
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12
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Ireland MF, Lenal FC, Lorier AR, Loomes DE, Adachi T, Alvares TS, Greer JJ, Funk GD. Distinct receptors underlie glutamatergic signalling in inspiratory rhythm-generating networks and motor output pathways in neonatal rat. J Physiol 2008; 586:2357-70. [PMID: 18339693 DOI: 10.1113/jphysiol.2007.150532] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Despite the enormous diversity of glutamate (Glu) receptors and advances in understanding recombinant receptors, native Glu receptors underlying functionally identified inputs in active systems are poorly defined in comparison. In the present study we use UBP-302, which antagonizes GluR5 subunit-containing kainate (KA) receptors at < or = 10 microm, but other KA and AMPA receptors at > or = 100 microm, and rhythmically active in vitro preparations of neonatal rat to explore the contribution of non-NMDA receptor signalling in rhythm-generating and motor output compartments of the inspiratory network. At 10 microm, UBP-302 had no effect on inspiratory burst frequency or amplitude. At 100 microm, burst amplitude recorded from XII, C1 and C4 nerve roots was significantly reduced, but frequency was unaffected. The lack of a frequency effect was confirmed when local application of UBP-302 (100 microm) into the pre-Bötzinger complex (preBötC) did not affect frequency but substance P evoked a 2-fold increase. A UBP-302-sensitive (10 microm), ATPA-evoked frequency increase, however, established that preBötC networks are sensitive to GluR5 activation. Whole-cell recordings demonstrated that XII motoneurons also express functional GluR5-containing KA receptors that do not contribute to inspiratory drive, and confirmed the dose dependence of UBP-302 actions on KA and AMPA receptors. Our data provide the first evidence that the non-NMDA (most probably AMPA) receptors mediating glutamatergic transmission within preBötC inspiratory rhythm-generating networks are pharmacologically distinct from those transmitting drive to inspiratory motoneurons. This differential expression may ultimately be exploited pharmacologically to separately counteract depression of central respiratory rhythmogenesis or manipulate the drive to motoneurons controlling airway and pump musculature.
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Affiliation(s)
- M F Ireland
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada
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13
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Hettes SR, Heyming TW, Stanley BG. Stimulation of lateral hypothalamic kainate receptors selectively elicits feeding behavior. Brain Res 2007; 1184:178-85. [DOI: 10.1016/j.brainres.2007.09.060] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2007] [Revised: 09/20/2007] [Accepted: 09/24/2007] [Indexed: 11/24/2022]
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14
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Mayer ML. Crystal structures of the GluR5 and GluR6 ligand binding cores: molecular mechanisms underlying kainate receptor selectivity. Neuron 2005; 45:539-52. [PMID: 15721240 DOI: 10.1016/j.neuron.2005.01.031] [Citation(s) in RCA: 217] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Revised: 12/29/2004] [Accepted: 01/03/2005] [Indexed: 10/25/2022]
Abstract
Little is known about the molecular mechanisms underlying differences in the ligand binding properties of AMPA, kainate, and NMDA subtype glutamate receptors. Crystal structures of the GluR5 and GluR6 kainate receptor ligand binding cores in complexes with glutamate, 2S,4R-4-methylglutamate, kainate, and quisqualate have now been solved. The structures reveal that the ligand binding cavities are 40% (GluR5) and 16% (GluR6) larger than for GluR2. The binding of AMPA- and GluR5-selective agonists to GluR6 is prevented by steric occlusion, which also interferes with the high-affinity binding of 2S,4R-4-methylglutamate to AMPA receptors. Strikingly, the extent of domain closure produced by the GluR6 partial agonist kainate is only 3 degrees less than for glutamate and 11 degrees greater than for the GluR2 kainate complex. This, together with extensive interdomain contacts between domains 1 and 2 of GluR5 and GluR6, absent from AMPA receptors, likely contributes to the high stability of GluR5 and GluR6 kainate complexes.
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Affiliation(s)
- Mark L Mayer
- Porter Neuroscience Research Center, National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, USA.
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15
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Lee CJ, Labrakakis C, Joseph DJ, Macdermott AB. Functional similarities and differences of AMPA and kainate receptors expressed by cultured rat sensory neurons. Neuroscience 2005; 129:35-48. [PMID: 15489026 DOI: 10.1016/j.neuroscience.2004.07.015] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/08/2004] [Indexed: 11/22/2022]
Abstract
Dorsal root ganglion neurons express functional AMPA and kainate receptors near their central terminals. Activation of these receptors causes a decrease in glutamate release during action potential evoked synaptic transmission. Due to differences in kinetic properties and expression patterns of these two families of glutamate receptors in subpopulations of sensory neurons, AMPA and kainate receptors are expected to function differently. We used embryonic dorsal root ganglion (DRG) neurons maintained in culture to compare functional properties of kainate and AMPA receptors. Most DRG neurons in culture expressed kainate receptors and about half also expressed AMPA receptors. Most AMPA and kainate receptor-expressing DRG neurons were sensitive to capsaicin, suggesting involvement of these glutamate receptors in nociception. When activated by kainate, AMPA receptors were capable of driving a sustained train of action potentials while kainate receptors tended to activate action potential firing more transiently. Glutamate elicited more action potentials and a larger steady-state depolarization in neurons expressing both AMPA and kainate receptors than in neurons expressing only kainate receptors. Adding to their more potent activation properties, AMPA receptors recovered from desensitization much more quickly than kainate receptors. Activation of presynaptic receptors by low concentrations of kainate, but not ATPA, caused a tetrodotoxin-sensitive increase in the frequency of spontaneous EPSCs recorded in dorsal horn neurons. By recording synaptic pairs of DRG and dorsal horn neurons, we found that activation of presynaptic kainate and AMPA receptors decreased evoked glutamate release from terminals of DRG neurons in culture. Our data suggest that the endogenous ligand, glutamate, will cause a different physiological impact when activating these two types of non-NMDA glutamate receptors at central or peripheral nerve endings of sensory neurons.
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MESH Headings
- Action Potentials/drug effects
- Action Potentials/physiology
- Animals
- Capsaicin/pharmacology
- Cells, Cultured
- Embryo, Mammalian
- Excitatory Postsynaptic Potentials/drug effects
- Excitatory Postsynaptic Potentials/physiology
- Ganglia, Spinal/drug effects
- Ganglia, Spinal/physiology
- Glutamic Acid/metabolism
- Glutamic Acid/pharmacology
- Neurons, Afferent/drug effects
- Neurons, Afferent/physiology
- Patch-Clamp Techniques
- Rats
- Receptors, AMPA/drug effects
- Receptors, AMPA/metabolism
- Receptors, Kainic Acid/drug effects
- Receptors, Kainic Acid/metabolism
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Affiliation(s)
- C J Lee
- Department of Physiology and Cellular Biophysics and the Center for Neurobiology and Behavior, Columbia University, 630 West 168(th) Street BB1106, New York, NY 10032, USA
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16
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Alt A, Weiss B, Ogden AM, Knauss JL, Oler J, Ho K, Large TH, Bleakman D. Pharmacological characterization of glutamatergic agonists and antagonists at recombinant human homomeric and heteromeric kainate receptors in vitro. Neuropharmacology 2004; 46:793-806. [PMID: 15033339 DOI: 10.1016/j.neuropharm.2003.11.026] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2003] [Revised: 11/19/2003] [Accepted: 11/25/2003] [Indexed: 11/29/2022]
Abstract
An increasing body of evidence suggests that native kainate receptors form ion channels from homomeric and heteromeric combinations of five receptor subunits: GluR5, GluR6, GluR7, KA1 and KA2. We have examined the activity of agonists and antagonists at recombinant human kainate receptors expressed in HEK293 cells, using both whole-cell electrophysiological recording and 96-well plate fluo-3 based calcium microfluorimetry (FLIPR). Both homomeric (GluR5 and GluR6) and heteromeric (GluR5/6, GluR5/KA2 and GluR6/KA2) receptors were examined. Heteromeric receptor assemblies showed electrophysiological and pharmacological profiles which were distinct from homomeric channels. Several agonists, including AMPA, ATPA and (S)-5-iodowillardiine, and antagonists, including gamma-D-glutamylaminomethylsulphonic acid (GAMS) and the decahydroisoquinoline compounds LY293558, LY377770 and LY382884, were found to act at GluR5-containing channels while having no effect at GluR6 homomers. AMPA, ATPA and (S)-5-iodowillardiine did activate GluR6/KA2 heteromers, but only as partial agonists. Additionally, ATPA was shown to act as an antagonist at homomeric GluR6 receptors at high concentrations (IC50 approximately 2 mM). Kynurenic acid was also found to differentiate between GluR6 and GluR6/KA2 receptors, antagonizing glutamate at GluR6 (IC50 = 0.4 mM), while having no effect at GluR6/KA2 channels. The results of the current study provide a broad pharmacological characterization of both homomeric and heteromeric recombinant human kainate receptors, and identify which compounds are likely to be useful tools for studying these various receptor subtypes.
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Affiliation(s)
- A Alt
- Lilly Research Laboratories, Eli Lilly and Company, Neuroscience Discovery Research, Lilly Corporate Center, Indianapolis, IN 46285, USA.
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17
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Youn DH, Randic M. Modulation of excitatory synaptic transmission in the spinal substantia gelatinosa of mice deficient in the kainate receptor GluR5 and/or GluR6 subunit. J Physiol 2004; 555:683-98. [PMID: 14724198 PMCID: PMC1664855 DOI: 10.1113/jphysiol.2003.057570] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2003] [Accepted: 01/05/2004] [Indexed: 11/08/2022] Open
Abstract
Functional kainate (KA) receptors (KARs) are expressed in the spinal cord substantia gelatinosa (SG) region, and their activation has a capacity to modulate excitatory synaptic transmission at primary afferent synapses with SG neurones. In the present study, we have used gene-targeted mice lacking KAR GluR5 and/or GluR6 subunits to determine the identity of the receptor subunits involved in the KA-induced modulation of excitatory transmission. Our findings reveal that KARs comprising GluR5 or GluR6 subunits can either suppress or facilitate glutamatergic excitatory transmission in the SG of acutely prepared adult mouse spinal cord slices. In the absence of synaptic inhibition mediated by GABA(A) and glycine receptors, a biphasic effect of kainate is characteristic with facilitation apparent at a low concentration (30 nM) and depression at a higher concentration (3 microM). In addition, GluR6-KARs, localizing pre- and postsynaptically, are critically involved in inhibiting transmission at both A delta and C fibre monosynaptic pathways, whereas presynaptic GluR5-KARs play a limited role in inhibiting the C fibre-activated pathway. The results obtained support the hypothesis that KARs are involved in bi-directional regulation of excitatory synaptic transmission in the spinal cord SG region, and that these actions may be of critical importance for nociception and the clinical treatment of pain.
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Affiliation(s)
- Dong-Ho Youn
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
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18
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Valgeirsson J, Christensen JK, Kristensen AS, Pickering DS, Nielsen B, Fischer CH, Bräuner-Osborne H, Nielsen EØ, Krogsgaard-Larsen P, Madsen U. Synthesis and in vitro pharmacology at AMPA and kainate preferring glutamate receptors of 4-heteroarylmethylidene glutamate analogues. Bioorg Med Chem 2003; 11:4341-9. [PMID: 13129570 DOI: 10.1016/s0968-0896(03)00485-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
2-Amino-3-[3-hydroxy-5-(2-thiazolyl)-4-isoxazolyl]propionic acid (1) is a potent AMPA receptor agonist with moderate affinity for native kainic acid (KA) receptors, whereas (S)-E-4-(2,2-dimethylpropylidene)glutamic acid (3) show high affinity for the GluR5 subtype of KA receptors and much lower affinity for the GluR2 subtype of AMPA receptors. As an attempt to develop new pharmacological tools for studies of GluR5 receptors, (S)-E-4-(2-thiazolylmethylene)glutamic acid (4a) was designed as a structural hybrid between 1 and 3. 4a was shown to be a potent GluR5 agonist and a high affinity ligand and to indiscriminately bind to the AMPA receptor subtypes GluR1-4 with lower affinities. Compounds 4b-h, in which the 2-thiazolyl substituent of 4a was replaced by other heterocyclic rings, which have previously been incorporated as 5-substituents in AMPA analogues, as exemplified by 1 were also synthesized. Compounds 4b-h were either inactive (4e,f) or weaker than 4a as affinity ligands for GluR1-4 and GluR5 with relative potencies comparable with those of the corresponding AMPA analogues as AMPA receptor agonists. Compounds 4a-h may be useful tools for the progressing pharmacophore mapping of the GluR5 agonist binding site.
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Affiliation(s)
- Jon Valgeirsson
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark
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19
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Vivó M, Camón L, de Vera N, Martínez E. Lesion of substantia nigra pars compacta by the GluR5 agonist ATPA. Brain Res 2002; 955:104-14. [PMID: 12419526 DOI: 10.1016/s0006-8993(02)03373-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
UNLABELLED Dopamine (DA) released by substantia nigra pars compacta (SNc) neurons is a key regulator of motor activity. A deficiency in the striatum DA content due to SNc degeneration is a characteristic of Parkinson's disease. The involvement of excitotoxic mechanisms in this pathology has been suggested. The kainate receptor subunit GluR5 has been identified in a few basal ganglia but it is strongly expressed in SNc. Here we examine whether (RS)-2-amino-3-(3-hydroxy-5-tbutylisoxazol-4-yl) propanoic acid (ATPA), a selective agonist of GluR5, induces damage in dopaminergic (DAergic) neurons. ATPA (13 nmol) was administered to rat SNc. Immediately after recovery from surgery, the rats displayed ipsilateral turning. This behavior disappeared in subsequent days. The administration of the D1/D2 agonist, apomorphine (1 mg/kg, s.c.) 1 and 2 weeks after ATPA-infusion also induced ipsilateral turning. Histological studies-performed 21 days after ATPA-infusion-showed a lesion of the lateral and central part of the SNc, where a significant loss (36%) of DAergic cells was detected by tyrosine hydroxylase immunohistochemistry. The lesion was restricted to the SNc, since no damage or glial reaction was observed in the substantia nigra pars reticulata as assessed by Nissl staining, tomato lectin staining for microglial cells and GFAP immunohistochemistry for astrocytes. IN CONCLUSION (1). ATPA-infusion induces neuronal damage in the SNc in the rat and (2). the behavioral effects of unilateral infusion of ATPA are consistent with DAergic alterations in basal ganglia.
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Affiliation(s)
- Meritxell Vivó
- Department of Neurochemistry, Institut d'Investigacions Biomèdiques de Barcelona (CSIC-IDIBAPS), E08036, Barcelona, Spain
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20
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Carpenedo R, Pittaluga A, Cozzi A, Attucci S, Galli A, Raiteri M, Moroni F. Presynaptic kynurenate-sensitive receptors inhibit glutamate release. Eur J Neurosci 2001; 13:2141-7. [PMID: 11422455 DOI: 10.1046/j.0953-816x.2001.01592.x] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Kynurenic acid is a tryptophan metabolite provided with antagonist activity on ionotropic glutamate and alpha7 nicotinic acetylcholine receptors. We noticed that in rats with a dialysis probe placed in the head of their caudate nuclei, local administration of kynurenic acid (30-100 nM) significantly reduced glutamate output. Qualitatively and quantitatively similar effects were observed after systemic administration of kynurenine hydroxylase inhibitors, a procedure able to increase brain kynurenate concentrations. Interestingly, in microdialysis studies, methyllycaconitine (0.3-10 nM), a selective alpha7 nicotinic receptor antagonist, also reduced glutamate output. In isolated superfused striatal synaptosomes, kynurenic acid (100 nM), but not methyllycaconitine, inhibited the depolarization (KCl 12.5 mM)-induced release of transmitter or previously taken-up [3H]-D-aspartate. This inhibition was not modified by glycine, N-methyl-D-aspartate or subtype-selective kainate receptor agents, while CNQX or DNQX (10 microM), two AMPA and kainate receptor antagonists, reduced kynurenic acid effects. Low concentrations of kynurenic acid, however, did not modify [3H]-kainate (high and low affinity) or [3H]-AMPA binding to rat brain membranes. Finally, because metabotropic glutamate (mGlu) receptors modulate transmitter release in striatal preparations, we evaluated, with negative results, kynurenic acid (1-100 nM) effects in cells transfected with mGlu1, mGlu2, mGlu4 or mGlu5 receptors. In conclusion, our data show that kynurenate-induced inhibition of glutamate release is not mediated by glutamate receptors. Nicotinic acetylcholine receptors, however, may contribute to the inhibitory effects of kynurenate found in microdialysis studies, but not in those found in isolated synaptosomes.
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Affiliation(s)
- R Carpenedo
- Department of Preclinical and Clinical Pharmacology, Viale Pieraccini 6, University of Florence, 50139 Florence, Italy
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21
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Bunch L, Johansen TH, Bräuner-Osborne H, Stensbøl TB, Johansen TN, Krogsgaard-Larsen P, Madsen U. Synthesis and receptor binding affinity of new selective GluR5 ligands. Bioorg Med Chem 2001; 9:875-9. [PMID: 11354670 DOI: 10.1016/s0968-0896(00)00304-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Two hybrid analogues of the kainic acid receptor agonists, 2-amino-3-(5-tert-butyl-3-hydroxy-4-isoxazolyl)propionic acid (ATPA) and (2S,4R)-4-methylglutamic acid ((2S,4R)-4-Me-Glu), were designed, synthesized, and characterized in radioligand binding assays using cloned ionotropic and metabotropic glutamic acid receptors. The (S)-enantiomers of E-4-(2,2-dimethylpropylidene)glutamic acid ((S)-1) and E-4-(3,3-dimethylbutylidene)glutamic acid ((S)-2) were shown to be selective and high affinity GluR5 ligands, with Ki values of 0.024 and 0.39 microM, respectively, compared to Ki values at GluR2 of 3.0 and 2.0 microM. respectively. Their affinities in the [3H]AMPA binding assay on native cortical receptors were shown to correlate with their GluR2 affinity rather than their GluR5 affinity. No affinity for GluR6 was detected (IC50 > 100 microM).
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Affiliation(s)
- L Bunch
- Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, Universitetsparken 2, Copenhagen
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22
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Abstract
Small diameter dorsal root ganglion (DRG) neurons, which include cells that transmit nociceptive information into the spinal cord, are known to express functional kainate receptors. It is well established that exposure to kainate will depolarize C-fiber afferents arising from these cells. Although the role of kainate receptors on sensory afferents is unknown, it has been hypothesized that presynaptic kainate receptors may regulate glutamate release in the spinal cord. Here we show that kainate, applied at low micromolar concentrations in the presence of the AMPA-selective antagonist (RS)-4-(4-aminophenyl)-1, 2-dihydro-1-methyl-2-propyl-carbamoyl-6,7-methylenedioxyphthalazine++ +, suppressed spontaneous NMDA receptor-mediated EPSCs in cultures of spinal dorsal horn neurons. In addition, kainate suppressed EPSCs in dorsal horn neurons evoked by stimulation of synaptically coupled DRG cells in DRG-dorsal horn neuron cocultures. Interestingly, although the glutamate receptor subunit 5-selective kainate receptor agonist (RS)-2-alpha-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA) (2 micrometer) was able to suppress DRG-dorsal horn synaptic transmission to a similar extent as kainate (10 micrometer), it had no effect on excitatory transmission between dorsal horn neurons. Agonist applications revealed a striking difference between kainate receptors expressed by DRG and dorsal horn neurons. Whereas DRG cell kainate receptors were sensitive to both kainate and ATPA, most dorsal horn neurons responded only to kainate. Finally, in recordings from dorsal horn neurons in spinal slices, kainate and ATPA were able to suppress NMDA and AMPA receptor-mediated EPSCs evoked by dorsal root fiber stimulation. Together, these data suggest that kainate receptor agonists, acting at a presynaptic locus, can reduce glutamate release from primary afferent sensory synapses.
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23
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Stensbøl TB, Jensen HS, Nielsen B, Johansen TN, Egebjerg J, Frydenvang K, Krogsgaard-Larsen P. Stereochemistry and molecular pharmacology of (S)-thio-ATPA, a new potent and selective GluR5 agonist. Eur J Pharmacol 2001; 411:245-53. [PMID: 11164381 DOI: 10.1016/s0014-2999(00)00916-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
(RS)-2-Amino-3-(5-tert-butyl-3-hydroxy-4-isothiazolyl)propionic acid (thio-ATPA), a 3-isothiazolol analogue of (RS)-2-amino-3-(5-tert-butyl-3-hydroxy-4-isoxazolyl)propionic acid (ATPA), has previously been shown to be a relatively weak AMPA receptor agonist at native (S)-glutamic acid ((S)-Glu) receptors (EC(50)=14 microM), comparable in potency with ATPA (EC(50)=34 microM). Recent findings, that (S)-ATPA is a potent (EC(50)=0.48 microM) and selective agonist at homomerically expressed ionotropic GluR5, prompted us to resolve thio-ATPA using chiral chromatography and pharmacologically characterize the two enantiomers at native as well as cloned ionotropic glutamate receptors. The enantiomers, (S)- and (R)-thio-ATPA, were obtained in high enantiomeric excess, and their absolute stereochemistry established by an X-ray crystallographic analysis. Electrophysiologically, the two enantiomers were evaluated in the rat cortical wedge preparation, and the S-enantiomer was found to be an AMPA receptor agonist (EC(50)=8.7 microM) twice as potent as the racemate, whereas the R-enantiomer was devoid of activity. In accordance with this, (S)-thio-ATPA proved to be an agonist at homomerically expressed recombinant AMPA receptors (GluR1o, GluR3o, and GluR4o) with EC(50) values of 5, 32 and 20 microM, respectively, producing maximal steady state currents of 78--168% of those maximally evoked by kainic acid, and 120-1600% of those maximally evoked by (S)-ATPA. At homomerically expressed GluR5, (S)-thio-ATPA was found to be a potent agonist (EC(50)=0.10 microM), thus being approximately five times more potent than (S)-ATPA. (R)-Thio-ATPA induced saturating currents with an estimated EC(50) value of 10 microM, most likely due to a contamination with (S)-thio-ATPA. At heteromerically expressed GluR6+KA2 receptors, (S)-thio-ATPA showed relatively weak agonistic properties (EC(50)=4.9 microM). Thus, (S)-thio-ATPA has been shown to be a very potent agonist at GluR5, and may be a valuable tool for the investigation of desensitization properties of AMPA receptors.
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Affiliation(s)
- T B Stensbøl
- NeuroScience PharmaBiotec Research Center, Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, 2 Universitetsparken, DK-2100 Copenhagen, Denmark
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24
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Lees GJ. Pharmacology of AMPA/kainate receptor ligands and their therapeutic potential in neurological and psychiatric disorders. Drugs 2000; 59:33-78. [PMID: 10718099 DOI: 10.2165/00003495-200059010-00004] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
It has been postulated, consistent with the ubiquitous presence of glutamatergic neurons in the brain, that defects in glutamatergic neurotransmission are associated with many human neurological and psychiatric disorders. This review evaluates the possible application of ligands acting on glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and kainate (KA) receptors to minimise the pathology and/or symptoms of various diseases. Glutamate activation of AMPA receptors is thought to mediate most fast synaptic neurotransmission in the brain, while transmission via KA receptors contributes only a minor component. Variants of the protein subunits forming these receptors greatly extend the pharmacological and electrophysiological properties of AMPA/KA receptors. Disease and drug use can differentially affect the expression of the subunits and their variants. Ligands bind to AMPA receptors by competing with glutamate at the glutamate binding site, or non-competitively at other sites on the proteins (allosteric modulators). Ligands showing selective competitive antagonist actions at the AMPA/ KA class of glutamate receptors were first reported in 1988, and the systemically active antagonist 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX) was first shown to have useful therapeutic effects on animal models of neurological diseases in 1990. Since then, newer antagonists with increased potency, higher specificity, increased water solubility, and a longer duration of action in vivo have been developed. Negative allosteric modulators such as the prototype GYKI-52466 also block AMPA receptors but have little action at KA receptors. Positive allosteric modulators enhance glutamatergic neurotransmission at AMPA receptors. Polyamines and adamantane derivatives bind within the ion channel of calcium-permeable AMPA receptors. The latest developments include ligands selective for KA receptors containing Glu-R5 subunits. Evidence for advantages of AMPA receptor antagonists over N-methyl-D-aspartate (NMDA) receptor antagonists for symptomatic treatment of neurological and psychiatric conditions, and for minimising neuronal loss occurring after acute neurological diseases, such as physical trauma, ischaemia or status epilepticus, have been shown in animal models. However, as yet AMPA receptor antagonists have not been shown to be effective in clinical trials. On the other hand, a limited number of clinical trials have been reported for AMPA receptor ligands that enhance glutamatergic neurotransmission by extending the ion channel opening time (positive allosteric modulators). These acute studies demonstrate enhanced memory capability in both young and aged humans, without any apparent serious adverse effects. The use of these allosteric modulators as antipsychotic drugs is also possible. However, the long term use of both direct agonists and positive allosteric modulators must be approached with considerable caution because of potential adverse effects.
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Affiliation(s)
- G J Lees
- Department of Psychiatry and Behavioural Science, University of Auckland School of Medicine, New Zealand.
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