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Bliss-Moreau E, Toscano JE, Bauman MD, Mason WA, Amaral DG. Neonatal amygdala lesions alter responsiveness to objects in juvenile macaques. Neuroscience 2011; 178:123-32. [PMID: 21215794 PMCID: PMC3962772 DOI: 10.1016/j.neuroscience.2010.12.038] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Revised: 12/16/2010] [Accepted: 12/21/2010] [Indexed: 11/19/2022]
Abstract
The amygdala is widely recognized to play a central role in emotional processing. In nonhuman primates, the amygdala appears to be critical for generating appropriate behavioral responses in emotionally salient contexts. One common finding is that macaque monkeys that receive amygdala lesions as adults are behaviorally uninhibited in the presence of potentially dangerous objects. While control animals avoid these objects, amygdala-lesioned animals readily interact with them. Despite a large literature documenting the role of the amygdala in emotional processing in adult rhesus macaques, little research has assessed the role of the amygdala across the macaque neurodevelopmental trajectory. We assessed the behavioral responses of 3-year-old (juvenile) rhesus macaques that received bilateral ibotenic acid lesions of the amygdala or hippocampus at 2 weeks of age. Animals were presented with salient objects known to produce robust fear-related responses in macaques (e.g., snakes and reptile-like objects), mammal-like objects that included animal-like features (e.g., eyes and mouths) but not reptile-like features (e.g., scales), and non-animal objects. The visual complexity of objects was scaled to vary the objects' salience. In contrast to control and hippocampus-lesioned animals, amygdala-lesioned animals were uninhibited in the presence of potentially dangerous objects. They readily retrieved food rewards placed near these objects and physically explored the objects. Furthermore, while control and hippocampus-lesioned animals differentiated between levels of object complexity, amygdala-lesioned animals did not. Taken together, these findings suggest that early damage to the amygdala, like damage sustained during adulthood, permanently compromises emotional processing.
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Affiliation(s)
- E Bliss-Moreau
- Department of Psychiatry and Behavioral Sciences, University of California, Davis, CA, USA
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2
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Clausen RP, Naur P, Kristensen AS, Greenwood JR, Strange M, Bräuner-Osborne H, Jensen AA, Nielsen AST, Geneser U, Ringgaard LM, Nielsen B, Pickering DS, Brehm L, Gajhede M, Krogsgaard-Larsen P, Kastrup JS. The glutamate receptor GluR5 agonist (S)-2-amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid and the 8-methyl analogue: synthesis, molecular pharmacology, and biostructural characterization. J Med Chem 2009; 52:4911-22. [PMID: 19588945 DOI: 10.1021/jm900565c] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The design, synthesis, and pharmacological characterization of a highly potent and selective glutamate GluR5 agonist is reported. (S)-2-Amino-3-((RS)-3-hydroxy-8-methyl-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid (5) is the 8-methyl analogue of (S)-2-amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid ((S)-4-AHCP, 4). Compound 5 displays an improved selectivity profile compared to 4. A versatile stereoselective synthetic route for this class of compounds is presented along with the characterization of the binding affinity of 5 to ionotropic glutamate receptors (iGluRs). Functional characterization of 5 at cloned iGluRs using a calcium imaging assay and voltage-clamp recordings show a different activation of GluR5 compared to (S)-glutamic acid (Glu), kainic acid (KA, 1), and (S)-2-amino-3-(3-hydroxy-5-tert-butyl-4-isoxazolyl)propionic acid ((S)-ATPA, 3) as previously demonstrated for 4. An X-ray crystallographic analysis of 4 and computational analyses of 4 and 5 bound to the GluR5 agonist binding domain (ABD) are presented, including a watermap analysis, which suggests that water molecules in the agonist binding site are important selectivity determinants.
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Affiliation(s)
- Rasmus P Clausen
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.
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3
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Bunch L, Krogsgaard-Larsen P. Subtype selective kainic acid receptor agonists: Discovery and approaches to rational design. Med Res Rev 2009; 29:3-28. [DOI: 10.1002/med.20133] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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4
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Nielsen BB, Pickering DS, Greenwood JR, Brehm L, Gajhede M, Schousboe A, Kastrup JS. Exploring the GluR2 ligand-binding core in complex with the bicyclical AMPA analogue (S)-4-AHCP. FEBS J 2005; 272:1639-48. [PMID: 15794751 DOI: 10.1111/j.1742-4658.2005.04583.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The X-ray structure of the ionotropic GluR2 ligand-binding core (GluR2-S1S2J) in complex with the bicyclical AMPA analogue (S)-2-amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]-4-isoxazolyl)propionic acid [(S)-4-AHCP] has been determined, as well as the binding pharmacology of this construct and of the full-length GluR2 receptor. (S)-4-AHCP binds with a glutamate-like binding mode and the ligand adopts two different conformations. The K(i) of (S)-4-AHCP at GluR2-S1S2J was determined to be 185 +/- 29 nM and at full-length GluR2(R)o it was 175 +/- 8 nM. (S)-4-AHCP appears to elicit partial agonism at GluR2 by inducing an intermediate degree of domain closure (17 degrees). Also, functionally (S)-4-AHCP has an efficacy of 0.38 at GluR2(Q)i, relative to (S)-glutamate. The proximity of bound (S)-4-AHCP to domain D2 prevents full D1-D2 domain closure, which is limited by steric repulsion, especially between Leu704 and the ligand.
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Affiliation(s)
- Bettina B Nielsen
- Biostructural Research, Department of Medicinal Chemistry, Danish University of Pharmaceutical Sciences, Copenhagen, Denmark
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5
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Brehm L, Greenwood JR, Hansen KB, Nielsen B, Egebjerg J, Stensbøl TB, Bräuner-Osborne H, Sløk FA, Kronborg TTA, Krogsgaard-Larsen P. (S)-2-Amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid, a potent and selective agonist at the GluR5 subtype of ionotropic glutamate receptors. Synthesis, modeling, and molecular pharmacology. J Med Chem 2003; 46:1350-8. [PMID: 12672235 DOI: 10.1021/jm0204441] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have previously described (RS)-2-amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid (4-AHCP) as a highly effective agonist at non-N-methyl-d-aspartate (non-NMDA) glutamate (Glu) receptors in vivo, which is more potent than (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) but inactive at NMDA receptors. However, 4-AHCP was found to be much weaker than AMPA as an inhibitor of [(3)H]AMPA binding and to have limited effect in a [(3)H]kainic acid binding assay using rat cortical membranes. To shed light on the mechanism(s) underlying this quite enigmatic pharmacological profile of 4-AHCP, we have now developed a synthesis of (S)-4-AHCP (6) and (R)-4-AHCP (7). At cloned metabotropic Glu receptors mGluR1alpha (group I), mGluR2 (group II), and mGluR4a (group III), neither 6 nor 7 showed significant agonist or antagonist effects. The stereoisomer 6, but not 7, activated cloned AMPA receptor subunits GluR1o, GluR3o, and GluR4o with EC(50) values in the range 4.5-15 microM and the coexpressed kainate-preferring subunits GluR6 + KA2 (EC(50) = 6.4 microM). Compound 6, but not 7, proved to be a very potent agonist (EC(50) = 0.13 microM) at the kainate-preferring GluR5 subunit, equipotent with (S)-2-amino-3-(5-tert-butyl-3-hydroxyisothiazol-4-yl)propionic acid [(S)-Thio-ATPA, 4] and almost 4 times more potent than (S)-2-amino-3-(5-tert-butyl-3-hydroxyisoxazol-4-yl)propionic acid [(S)-ATPA, 3]. Compound 6 thus represents a new structural class of GluR5 agonists. Molecular modeling and docking to a crystal structure of the extracellular binding domain of the AMPA subunit GluR2 has enabled identification of the probable active conformation and binding mode of 6. We are able to rationalize the observed selectivities by comparing the docking of 4 and 6 to subtype constructs, i.e., a crystal structure of the extracellular binding domain of GluR2 and a homology model of GluR5.
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Affiliation(s)
- Lotte Brehm
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark
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6
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Bräuner-Osborne H, Egebjerg J, Nielsen EO, Madsen U, Krogsgaard-Larsen P. Ligands for glutamate receptors: design and therapeutic prospects. J Med Chem 2000; 43:2609-45. [PMID: 10893301 DOI: 10.1021/jm000007r] [Citation(s) in RCA: 463] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
MESH Headings
- Animals
- Drug Design
- Excitatory Amino Acid Agonists/chemistry
- Excitatory Amino Acid Agonists/metabolism
- Excitatory Amino Acid Agonists/pharmacology
- Excitatory Amino Acid Agonists/therapeutic use
- Excitatory Amino Acid Antagonists/chemistry
- Excitatory Amino Acid Antagonists/metabolism
- Excitatory Amino Acid Antagonists/pharmacology
- Excitatory Amino Acid Antagonists/therapeutic use
- Humans
- Ligands
- N-Methylaspartate/agonists
- N-Methylaspartate/antagonists & inhibitors
- N-Methylaspartate/chemistry
- N-Methylaspartate/metabolism
- Receptors, AMPA/agonists
- Receptors, AMPA/antagonists & inhibitors
- Receptors, AMPA/chemistry
- Receptors, AMPA/metabolism
- Receptors, Glutamate/chemistry
- Receptors, Glutamate/drug effects
- Receptors, Glutamate/metabolism
- Receptors, Kainic Acid/agonists
- Receptors, Kainic Acid/antagonists & inhibitors
- Receptors, Kainic Acid/chemistry
- Receptors, Kainic Acid/metabolism
- Receptors, Metabotropic Glutamate/agonists
- Receptors, Metabotropic Glutamate/antagonists & inhibitors
- Receptors, Metabotropic Glutamate/chemistry
- Receptors, Metabotropic Glutamate/metabolism
- Synapses/metabolism
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Affiliation(s)
- H Bräuner-Osborne
- NeuroScience PharmaBiotec Research Center, Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, DK-2100 Copenhagen, Denmark
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7
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Riess R, Schön M, Laschat S, Jäger V. Evaluation of Protecting Groups for 3-Hydroxyisoxazoles − Short Access to 3-Alkoxyisoxazole-5-carbaldehydes and 3-Hydroxyisoxazole-5-carbaldehyde, the Putative Toxic Metabolite of Muscimol. European J Org Chem 1998. [DOI: 10.1002/(sici)1099-0690(199803)1998:3<473::aid-ejoc473>3.0.co;2-v] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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8
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9
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Schultz AG, Wang A. Hydrophenanthrene Construction by Aryl Radical Cyclization. Synthesis of 2,3,4,4a,9,10-Hexahydro-7-methoxy- 4a-methylphenanthren-2-one. J Org Chem 1996; 61:4857-4859. [PMID: 11667431 DOI: 10.1021/jo9605410] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Arthur G. Schultz
- Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 12180-3590
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10
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López A, Moreno-Mañas M, Pleixats R, Roglans A, Ezquerra J, Pedregal C. Ethyl N-(diphenylmethylene)glycinate as anionic glycine equivalent. Monoalkylation, dialkylation and Michael additions under solid-liquid phase-transfer catalysis. Tetrahedron 1996. [DOI: 10.1016/0040-4020(96)00395-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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11
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Pelletier JC, Hesson DP, Jones KA, Costa AM. Substituted 1,2-dihydrophthalazines: potent, selective, and noncompetitive inhibitors of the AMPA receptor. J Med Chem 1996; 39:343-6. [PMID: 8558499 DOI: 10.1021/jm950740w] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- J C Pelletier
- Symphony Pharmaceuticals, Malvern, Pennsylvania 19355, USA
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12
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Krogsgaard-Larsen P, Ebert B, Lund TM, Bräuner-Osborne H, Sløk FA, Johansen TN, Brehm L, Madsen U. Design of excitatory amino acid receptor agonists, partial agonists and antagonists: ibotenic acid as a key lead structure. Eur J Med Chem 1996. [DOI: 10.1016/0223-5234(96)89549-3] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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13
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14
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Moreno-Man˜as M, Pérez M, Pleixats R. Palladium-catalyzed allylation of 3-hydroxyisoxazole, 5-isoxazolone and 5-pyrazolone Systems. Tetrahedron 1994. [DOI: 10.1016/s0040-4020(01)80773-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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15
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Madsen U, Frølund B, Lund TM, Ebert B, Krogsgaard-Larsen P. Design, synthesis and pharmacology of model compounds for indirect elucidation of the topography of AMPA receptor sites. Eur J Med Chem 1993. [DOI: 10.1016/0223-5234(93)90114-t] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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16
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Krogsgaard-Larsen P. GABA and glutamate receptors as therapeutic targets in neurodegenerative disorders. ACTA ACUST UNITED AC 1992; 70:95-104. [PMID: 1354863 DOI: 10.1111/j.1600-0773.1992.tb00436.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- P Krogsgaard-Larsen
- Department of Organic Chemistry, Royal Danish School of Pharmacy, Copenhagen
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17
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Carruth MK, Fowler AA, Fairman RP, Mayer DJ, Leichnetz GR. Respiratory failure without pulmonary edema following injection of a glutamate agonist into the ventral medullary raphe of the rat. Brain Res Bull 1992; 28:365-78. [PMID: 1375523 DOI: 10.1016/0361-9230(92)90036-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Injection of ibotenic acid (IA), a glutamate agonist, into the ventral medullary raphe (VMR; especially the nucleus raphe magnus) of the rat produced respiratory failure and death following a predictable course of events. The response to the IA injection was characterized initially by increased respiratory frequency and was followed by pulmonary arterial hypertension, systemic arterial hypoxemia, acidosis, and hypothermia. Within 90 min apnea occurred as a terminal event in all animals. Gravimetric, bronchoalveolar lavage protein, and histological analyses revealed no evidence of pulmonary edema. Intracerebral (VMR) pretreatment with PPP, a sigma receptor agonist, or scopolamine, a muscarinic cholinergic antagonist, prevented pulmonary failure and death even though postmortem histological analysis showed VMR cell loss and gliosis consequent to the cytotoxic IA injection. Based on the results of the study, it is suggested that the VMR has a role in regulation of pulmonary blood flow. Preliminary pharmacological studies suggested that a disruption of glutamatergic and cholinergic mechanisms mediates the lethal pulmonary phenomenon.
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Affiliation(s)
- M K Carruth
- Department of Anatomy, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298
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18
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Excitatory amino acid receptors: Multiplicity and ligand specificity of the NMDA and AMPA receptor subtypes. ACTA ACUST UNITED AC 1992. [DOI: 10.1016/b978-0-444-88931-7.50018-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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19
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Ebert B, Madsen U, Johansen TN, Krogsgaard-Larsen P. NMDA receptor agonists: relationships between structure and biological activity. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1991; 287:483-7. [PMID: 1836933 DOI: 10.1007/978-1-4684-5907-4_42] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- B Ebert
- Department of Organic Chemistry, Royal Danish School of Pharmacy, Copenhagen
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20
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Madsen U, Ferkany JW, Jones BE, Ebert B, Johansen TN, Holm T, Krogsgaard-Larsen P. NMDA receptor agonists derived from ibotenic acid. Preparation, neuroexcitation and neurotoxicity. Eur J Pharmacol 1990; 189:381-91. [PMID: 1963602 DOI: 10.1016/0922-4106(90)90035-v] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The two heterocyclic aspartic acid and glutamic acid analogues derived from ibotenic acid, (RS)-2-amino-2-(3-hydroxy-5-methylisoxazol-4-yl)acetic acid (AMAA) and (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) have previously been shown to be selective agonists at N-methyl-D-aspartic acid (NMDA) and AMPA receptors, respectively. Two analogous series of AMAA and AMPA derivatives have now been synthesized and characterized in receptor binding studies and neuropharmacological experiments. AMAA was shown to be a very potent NMDA agonist in cortical tissue preparations, slightly more active than NMDA, whereas N-methyl-AMAA was less potent and N,N-dimethyl-AMAA almost inactive. (RS)-3-Hydroxy-4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridine-4-carboxylic acid (4-HPCA), a bicyclic analogue of AMAA, exhibited weak NMDA agonist effects similar to those of quinolinic acid. The relative potency as AMPA receptor agonists of AMPA, N-methyl-AMPA, N,N-dimethyl-AMPA and (RS)-3-hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-5-carboxylic acid (5-HPCA), a bicyclic analogue of AMPA, was distinctly different from that of the AMAA series of compounds as NMDA agonists. The pharmacological and toxicological profiles of AMAA and 4-HPCA, compared with those of quinolinic acid, are consistent with heterogeneity of NMDA receptors.
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Affiliation(s)
- U Madsen
- Department of Organic Chemistry, Royal Danish School of Pharmacy, Copenhagen
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21
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Watkins JC, Krogsgaard-Larsen P, Honoré T. Structure-activity relationships in the development of excitatory amino acid receptor agonists and competitive antagonists. Trends Pharmacol Sci 1990; 11:25-33. [PMID: 2155495 DOI: 10.1016/0165-6147(90)90038-a] [Citation(s) in RCA: 695] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Development of new selective ligands for excitatory amino acid receptors has been fundamental in supporting this rapidly developing field. Some of the most important ligands have come from the laboratories of Jeff Watkins, Povl Krogsgaard-Larsen and Tage Honoré, who collaborate in this double-length review to describe the chemical features and SARs of agonists and antagonists, particularly those features associated with subtype selectivity.
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Affiliation(s)
- J C Watkins
- Department of Pharmacology, School of Medical Sciences, University Walk, Bristol
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22
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Hansen JJ, Krogsgaard-Larsen P. Structural, conformational, and stereochemical requirements of central excitatory amino acid receptors. Med Res Rev 1990; 10:55-94. [PMID: 2153264 DOI: 10.1002/med.2610100103] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- J J Hansen
- Department of Organic Chemistry, Royal Danish School of Pharmacy, Copenhagen
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23
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Excitatory amino acid receptors coupled to phosphoinositide metabolism: Characterization and possible role in physiology and physiopathology. Amino Acids 1990. [DOI: 10.1007/978-94-011-2262-7_27] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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24
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Cincotta M, Summers RJ, Beart PM. Biochemical characterization of an autoradiographic method for studying excitatory amino acid receptors using L-[3H]glutamate. Anal Biochem 1989; 177:150-5. [PMID: 2568102 DOI: 10.1016/0003-2697(89)90030-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A method was developed for radiolabeling excitatory amino acid receptors of rat brain with L-[3H]glutamate. Effective labeling of glutamate receptors in slide-mounted 10-microns sections was obtained using a low incubation volume (0.15 ml) and rapid washing: a procedure where high ligand concentrations were achieved with minimal waste. Saturation experiments using [3H]glutamate revealed a single binding site of micromolar affinity. The Bmax was trebled in the presence of Ca2+ (2.5 mM) and Cl- (20 mM) with no change in the Kd. Binding was rapid, saturable, stereospecific, and sensitive to glutamate receptor agonists. The proportions of [3H]glutamate binding sensitive to N-methyl-D-aspartate (NMDA), kainate, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were 34, 54, and 51%, respectively. NMDA inhibited binding at a distinct subset of L-[3H]glutamate sites, whereas AMPA and kainate competed for some common sites. Labeling of sections with L-[3H]glutamate in the presence of the selective agonists allowed autoradiographic visualization of glutamate receptor subtypes in brain tissue.
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Affiliation(s)
- M Cincotta
- University of Melbourne, Clinical Pharmacology and Therapeutics Unit, Austin Hospital, Heidelberg, Victoria, Australia
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25
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López-Colomé AM, Somohano F. Characterization of quisqualate-type L-glutamate receptors in the retina. Brain Res 1987; 414:99-108. [PMID: 2887240 DOI: 10.1016/0006-8993(87)91330-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In the vertebrate retina excitatory transmission seems to be mediated mainly by excitatory amino acids; glutamate and/or aspartate are the most viable candidates to subserve this function. Postsynaptic receptors for N-methyl-D-aspartate (NMDA), kainate (KA), quisqualate (QA) and 2-amino-4-phosphonobutyric acid have been electrophysiologically identified. In this work we have tried to identify and characterize QA receptors through the binding of the most specific analogue available for this receptor: [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA). AMPA binding to retinal membranes was sodium- and temperature-independent, with optimum pH at 6-7. Ligand-receptor interaction was reversible and saturable. Pharmacologically, glutamate analogues were more active displacers than NMDA analogues: AMPA greater than (RS)-3-hydroxy-4,5,6,7-tetrahydro-isoxazolo-(5,4-C)-pyridine-7-car boxylic acid = L-Glu = QA; with IC50 in the low microM range. Glutamic acid diethylester was uneffective while KA and cis-2,3-piperidine dicarboxylate were potent inhibitors of binding. Binding was stereospecific, L-isomers being more effective displacers than D-forms. Subcellular distribution showed binding concentrated in the inner plexiform layer (IPL), but also present in the outer plexiform layer (OPL). Kinetics of [3H]AMPA binding showed a high affinity kB = 1-2 microM in membranes from complete retina, IPL and OPL, with binding sites concentrated in P2 (Bmax = 16.2 pmol/mg protein). Our results provide biochemical evidence for the presence and distribution of physiologically relevant QA receptors in the chick retina which is in agreement with previous physiological findings.
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26
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Nielsen EO, Schousboe A, Hansen SH, Krogsgaard-Larsen P. Excitatory amino acids: studies on the biochemical and chemical stability of ibotenic acid and related compounds. J Neurochem 1985; 45:725-31. [PMID: 2863325 DOI: 10.1111/j.1471-4159.1985.tb04052.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The complex pharmacological profile (excitation/inhibition) of ibotenic acid on single neurons in the mammalian CNS prompted studies on the stability of ibotenic acid and a number of structurally related excitatory amino acids under different in vitro conditions in the presence or absence of enzymes. Ibotenic acid, (RS)-3-hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-7-carboxylic acid (7-HPCA), (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and (RS)-alpha-amino-3-hydroxy-4-bromo-5-isoxazolepropionic acid (4-Br-homoibotenic acid) were all inhibitors of (S)-glutamic acid decarboxylase (GAD) in mouse brain homogenates, but only ibotenic acid was shown to undergo decarboxylation during incubation with brain homogenates. The formation of the decarboxylated product, muscimol, which primarily occurred in a synaptosomal fraction, was dependent on the presence of pyridoxal-5-phosphate (PALP) and was inhibited by (S)-glutamic acid, 3-mercaptopropionic acid (3MPA), aminooxyacetic acid (AOAA), and allyglycine, suggesting that ibotenic acid is a substrate for GAD. The overall decomposition rate for ibotenic acid (8.7 nmol min-1 mg-1 of protein), which apparently embraces other reactions in addition to decarboxylation to muscimol, was higher than the rate of decarboxylation of (S)-glutamic acid (3.2 nmol min-1 mg-1 of protein). At pH 7.4 and 37 degrees C, but in the absence of enzymes, none of the excitatory amino acids under study underwent any detectable decomposition, whereas ibotenic acid and 7-HPCA, but not AMPA and 4-Br-homoibotenic acid, decomposed, partially by decarboxylation, at 100 degrees C in a pH-dependent manner. In the presence of liver homogenates, ibotenic acid was also shown to decompose.(ABSTRACT TRUNCATED AT 250 WORDS)
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Crooks SL, Freund RK, Halsrud DA, Koerner JF, Johnson RL. Antagonist activity of methyl-substituted analogues of 2-amino-4-phosphonobutanoic acid in the hippocampal slice. Brain Res 1985; 329:346-9. [PMID: 2983843 DOI: 10.1016/0006-8993(85)90547-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Four monomethyl-substituted analogues of 2-amino-4-phosphonobutanoic acid (APB), an antagonist of excitatory pathways in the central nervous system, were prepared in order to investigate the steric requirements of the APB receptor. Methyl groups were incorporated at the amino, alpha-, beta-, and gamma-positions. The beta- and gamma-methyl-substituted analogues of APB were found to be moderately potent antagonists in excitatory synapses of the hippocampal perforant path, as judged by extracellular recording techniques, while the N- and alpha-methyl-substituted analogues had much lower potencies. All of these APB analogues had very low potencies in the Schaffer collateral pathway. The APB receptors in the perforant path displayed more tolerance of methyl-substitution at the beta- and gamma-positions of APB than at the amino or alpha-positions in this system.
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