2201
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Elezgarai I, Benítez R, Mateos JM, Lázaro E, Osorio A, Azkue JJ, Bilbao A, Lingenhoehl K, Van Der Putten H, Hampson DR, Kuhn R, Knöpfel T, Grandes P. Developmental expression of the group III metabotropic glutamate receptor mGluR4a in the medial nucleus of the trapezoid body of the rat. J Comp Neurol 1999; 411:431-40. [PMID: 10413777 DOI: 10.1002/(sici)1096-9861(19990830)411:3<431::aid-cne6>3.0.co;2-r] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A preembedding immunocytochemical method for light microscopy was used to study the postnatal development of expression of the group III metabotropic glutamate receptor mGluR4a in the medial nucleus of the trapezoid body (MNTB) of the rat. Immunoreactivity for mGluR4a was localized in axonal endings wrapping the principal globular neurons in MNTB, known as calyces of Held. The percentage of calyces of Held immunoreactive for mGluR4a increased progressively from postnatal day 3 (PND3), showing the highest density of labeled calyces by PND9. From this postnatal age on, a gradual reduction in the number of mGluR4a-immunopositive calyces of Held was observed, reaching the lowest level of labeled profiles in adult tissue. The developmental expression of mGluR4a in calyces of Held correlates well with previous studies in young animals showing a modulation of synaptic neurotransmission by group III mGluRs in these giant excitatory synapses made on MNTB principal neurons. All these observations together suggest that the expression of mGluR4a mainly between PND7 and PND12 might be relevant to the maturation and modulation of synaptic transmission at the calyces of Held.
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Affiliation(s)
- I Elezgarai
- Department of Neurosciences, Faculty of Medicine and Dentistry, Basque Country University, 699-48080 Bilbao, Spain
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2202
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Laezza F, Doherty JJ, Dingledine R. Long-term depression in hippocampal interneurons: joint requirement for pre- and postsynaptic events. Science 1999; 285:1411-4. [PMID: 10464102 DOI: 10.1126/science.285.5432.1411] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Long-term depression (LTD) is a well-known form of synaptic plasticity of principal neurons in the mammalian brain. Whether such changes occur in interneurons is still controversial. CA3 hippocampal interneurons expressing Ca2+-permeable AMPA receptors exhibited LTD after tetanic stimulation of CA3 excitatory inputs. LTD was independent of NMDA receptors and required both Ca2+ influx through postsynaptic AMPA receptors and activation of presynaptic mGluR7-like receptors. These results point to the capability of interneurons to undergo plastic changes of synaptic strength through joint activation of pre- and postsynaptic glutamate receptors.
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Affiliation(s)
- F Laezza
- Neuroscience Graduate Program, Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA
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2203
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Koulen P, Kuhn R, Wässle H, Brandstätter JH. Modulation of the intracellular calcium concentration in photoreceptor terminals by a presynaptic metabotropic glutamate receptor. Proc Natl Acad Sci U S A 1999; 96:9909-14. [PMID: 10449793 PMCID: PMC22309 DOI: 10.1073/pnas.96.17.9909] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fast excitatory neurotransmission in the central nervous system is mediated through glutamate acting on ionotropic glutamate receptors. However, glutamate acting on metabotropic glutamate receptors (mGluRs) can also exert an inhibitory action. Here, we report by immunocytochemistry and physiology, to our knowledge, the first glutamate receptor to be found in terminals of photoreceptors in the mammalian retina-the group III metabotropic glutamate receptor mGluR8. Glutamate is the transmitter of photoreceptors, and thus mGluR8 functions as an autoreceptor. Activation of mGluR8 by the group III mGluR agonists L-2-amino-4-phosphonobutyrate and L-serine-O-phosphate, or by glutamate itself, evokes a decrease in the intracellular calcium ion concentration ([Ca(2+)](i)) in isolated photoreceptors. This effect is blocked by the group III mGluR antagonists (RS)-alpha-methyl-4-phosphonophenylglycine and (RS)-alpha-methylserine-O-phosphate. Agonists for other classes of glutamate receptors-N-methyl-D-aspartic acid, quisqualic acid, kainic acid, or (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-have no effect on the [Ca(2+)](i) in isolated photoreceptors. The down-regulation of the [Ca(2+)](i) in photoreceptors by mGluR8 provides evidence for an inhibitory feedback loop at the photoreceptor synapse in the mammalian retina. This negative feedback may be a mechanism for the fine adjustment of the light-regulated release of glutamate from photoreceptors and may serve as a safety device against excitotoxic levels of release at this tonic synapse. Such a mechanism may provide a model for feedback inhibition in other parts of the central nervous system.
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Affiliation(s)
- P Koulen
- Max-Planck-Institut für Hirnforschung, Abteilung für Neuroanatomie, Deutschordenstrasse 46, D-60528 Frankfurt am Main, Germany
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2204
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Abstract
Activation of metabotropic glutamate receptors (mGluRs) can result in long-lasting modulation of neuronal excitability. Multiple mGluR subtypes are localized within the rat thalamic reticular nucleus (TRN), and we have examined the effects of activating these different receptor subtypes on the excitability of these neurons using an in vitro slice preparation. Typical of most mGluR-sensitive preparations, the general mGluR agonist, (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD) produced a robust, long-lasting excitatory response. Surprisingly, ACPD produced a membrane hyperpolarization in some neurons. Using selective mGluR agonists, we found that activation of group II mGluRs produces the hyperpolarization, whereas the depolarization is mediated by group I mGluRs. While the polarity of the postsynaptic response (hyperpolarization vs depolarization) was dependent on the mGluR subtype activated, both actions appear to result from modification of a linear K(+) conductance. The inhibitory action of Glutamate, via group II mGluRs, provides an avenue for a disinhibitory effect that could have interesting consequences upon a well-investigated, model neuronal circuit, turning its assumed functional role upside down.
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2205
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Abstract
The regulation of glutamate (Glu) release from the excitatory input to dopamine cells in the ventral tegmental area (VTA) during acute withdrawal from morphine was studied in slices from animals treated for 6-7 d with morphine. EPSCs were inhibited by opioid agonists acting at micro-subtype receptors but not by selective delta- or kappa-subtype agonists. The opioid inhibition was reduced by 65% with the potassium channel blocker 4-aminopyridine (4-AP; 100 microM) and a 12-lipoxygenase inhibitor, baicalein (5 microM), suggesting that opioids acted via a transduction pathway involving activation of a voltage-dependent potassium conductance by lipoxygenase metabolites as has been shown in the periaqueductal gray (). During withdrawal, neither the potency nor the efficacy of D-Ala-Met-enkephalin-Gly-ol (DAMGO) were changed; however, the blockade of micro-opioid inhibition by both 4-AP and baicalein was reduced. In addition, the potency of baclofen to depress EPSCs by GABA-B receptors and the effects of the GABA-uptake inhibitor NO-711 (10 microM) were increased in withdrawn rats. Finally, group 2 (but not group 4 or 1) metabotropic glutamate receptor-mediated presynaptic inhibition was also enhanced in morphine-withdrawn rats. These results suggest that one of the consequences of withdrawal from chronic morphine is an enhanced presynaptic inhibition of the excitatory inputs to the dopamine cells of the VTA. Inhibition of glutamate release during acute withdrawal would add to the inhibition of dopamine cells that is mediated by an augmented release of GABA ().
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2206
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Abstract
Recent data showed that group I metabotropic glutamate receptors (mGluRs) are located perisynaptic to the postsynaptic specializations of asymmetric glutamatergic synapses in the cerebellum and hippocampus in rats. In the present study, we used immunogold labeling to elucidate the subsynaptic localization of group I mGluRs (mGluR1a and mGluR5) in the internal and external segments of the globus pallidus in monkeys. In contrast to hippocampal and cerebellar neurons, which receive massive glutamatergic inputs, dendrites of pallidal neurons are covered with GABAergic boutons from the striatum intermingled with a small proportion of glutamatergic terminals arising largely from the subthalamic nucleus. In line with previous data, mGluR1a and mGluR5 immunoreactivity was found at the edge of the postsynaptic specializations of asymmetric synapses established by subthalamic-like boutons in the monkey pallidum. However, a large proportion of gold particles were also seen in the main body of the postsynaptic specializations of symmetric synapses formed by striatal GABAergic terminals. These data raise questions about the possible sources of activation of these receptors and the potential roles of group I mGluRs in modulating GABAergic neurotransmission at striatopallidal synapses.
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2207
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Kolczewski S, Adam G, Stadler H, Mutel V, Wichmann J, Woltering T. Synthesis of heterocyclic enol ethers and their use as group 2 metabotropic glutamate receptor antagonists. Bioorg Med Chem Lett 1999; 9:2173-6. [PMID: 10465539 DOI: 10.1016/s0960-894x(99)00346-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Heterocyclic enol ethers of type 1 were studied with respect to the inhibition of 1S,3R-ACPD (10 microM)-stimulated GTP gamma35S binding on rat mGluR2 transfected cell membranes. The structure activity relationship with regard to the substitution pattern of the phenyl ring, the oxygen substituent and the nature of the heterocycle is discussed.
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Affiliation(s)
- S Kolczewski
- Pharma Division, Preclinical CNS Research, F. Hoffmann-La Roche Ltd., Basel.
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2208
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Aguilera P, Ortega A. Stat3 participates in the metabotropic glutamate signaling pathway in Bergmann glial cells. Neurochem Res 1999; 24:981-6. [PMID: 10478936 DOI: 10.1023/a:1021044424103] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Purkinje cells establish a glutamatergic synapse with the parallel fibers in the cerebellum. Bergmann glial cells surround this synapse. The transcription factor Stat3, highly expressed in cerebellum, is present in cultures of chick Bergmann glia. Treatment of these cells with L-glutamate induces the tyrosine-phosphorylation of Stat3. The maximal phosphorylation was observed after 15 min and by 30 min returned to basal levels. This effect correlated with Stat3 translocation to nucleus and the appearance of a retarded band in gel mobility shift assays. The effects observed with L-glutamate were mediated through metabotropic glutamate receptors. These results further support the notion that glial cells respond to L-glutamate through changes in the existing proteins and also in gene expression regulation.
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Affiliation(s)
- P Aguilera
- Departamento de Genética y Biología Molecular, CINVESTAV-IPN, México DF, Mexico
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2209
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Abstract
Discoveries made over the past 20 years have greatly improved our understanding of how the brain functions. This article focuses on the relation between memory and cellular mechanisms of neuronal and synaptic plasticity in the hippocampus. Several studies indicate that the hippocampal formation is a crucial element of the neurobiological bases of higher cognitive function. Severe damage to the hippocampal formation is known to produce seemingly permanent anterograde amnesia. A generally accepted hypothesis in neurobiology has been that long-lasting activity-dependent changes in the efficacy of synaptic transmission in the mammalian brain are considered to be of fundamental importance for the development of neural circuitry and for the storage of information. The most compelling and reliable model for such changes has been long-term potentiation (LTP) and long-term depression (LTD) in the hippocampus. Therefore, the possibility of the discovery and development of compounds that, by modulating hippocampal synaptic plasticity, would be useful for the management of dementia and amnesia.
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Affiliation(s)
- S Akhondzadeh
- Department of Pharmacology and Therapeutics, Institute of Medicinal Plants, Tehran, Iran.
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2210
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Pellicciari R, Costantino G. Metabotropic G-protein-coupled glutamate receptors as therapeutic targets. Curr Opin Chem Biol 1999; 3:433-40. [PMID: 10419848 DOI: 10.1016/s1367-5931(99)80064-7] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Metabotropic glutamate receptors have received considerable attention over the past decade in view of their relevance in multiple aspects of glutamatergic transmission. Recent advances in the molecular biology, pharmacology and medicinal chemistry of this family of G-protein-coupled receptors have led to therapeutic opportunities for subtype-selective modulators in brain disorders and diseases such as ischemia and schizophrenia.
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Affiliation(s)
- R Pellicciari
- Istituto di Chimica e Tecnologia del Farmaco, Via del Liceo 1, I-06123,Perugia, Italy.
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2211
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Micheli F, Di Fabio R, Marchioro C. Asymmetric synthesis of some substituted-3-phenyl prolines. FARMACO (SOCIETA CHIMICA ITALIANA : 1989) 1999; 54:461-4. [PMID: 10486913 DOI: 10.1016/s0014-827x(99)00052-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The asymmetric synthesis of carboxyphenyl prolines was performed according to Schöllkopf methodology, to prepare possible antagonists of the metabotropic glutamate receptor mGluR1.
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Affiliation(s)
- F Micheli
- Glaxo Wellcome S.p.A., Medicines Research Centre, Verona, Italy.
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2212
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Kingston AE, O'Neill MJ, Lam A, Bales KR, Monn JA, Schoepp DD. Neuroprotection by metabotropic glutamate receptor glutamate receptor agonists: LY354740, LY379268 and LY389795. Eur J Pharmacol 1999; 377:155-65. [PMID: 10456425 DOI: 10.1016/s0014-2999(99)00397-0] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
In rat cortical neuronal cultures, metabotropic glutamate (mGlu) receptor agonists: LY354740 (+)-2-aminobicyclo[3.1.0]hexane-2,6dicarboxylate); LY379268 (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate, and LY389795 (-)-2-thia-4-aminobicyclo[3.1.0]-hexane-4,6-dicarboxylate, were neuroprotective against toxicity induced by N-methyl-D-aspartic acid (NMDA), kainic acid and staurosporine as measured by release of lactate dehydrogenase (LDH) activity into culture supernatants and DNA fragmentation by oligonucleosome formation. The potencies of the agonists were at least 100 times greater in reducing nucleosome formation than LDH release indicating a differential effect on neurons dying by apoptosis than by necrosis. In vivo studies showed that LY354740 was able to mediate a partial protection against apoptosis in CA1 hippocampal cells under ischaemic conditions where substantial CA1 cell loss occurred. The effects of the agonists in vitro were: (a) reversed by mGlu receptor antagonist LY341495, (b) enhanced by the presence of glial cells, (c) abrogated by RNA and protein synthesis inhibitors, and (d) unaltered by inhibition of endogenous adenosine activity. These results suggest that group II mGlu receptor agonists may represent a novel therapeutic strategy for the treatment of neurodegenerative diseases.
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Affiliation(s)
- A E Kingston
- Eli Lilly, Lilly Research Centre, Erl Wood Manor, Windlesham, Surrey, UK.
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2213
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Kommers T, Rodnight R, Oppelt D, Oliveira D, Wofchuk S. The mGluR stimulating GFAP phosphorylation in immature hippocampal slices has some properties of a group II receptor. Neuroreport 1999; 10:2119-23. [PMID: 10424685 DOI: 10.1097/00001756-199907130-00023] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In a previous study we showed that phosphorylation of the astrocytic marker glial fibrillary acidic protein (GFAP) in hippocampal slices from immature rats (P12-P16) is regulated by a metabotropic glutamate receptor (mGluR). The subtypes of these receptors are divided into three groups and exhibit two distinct transduction signals: activation of phospholipase C and liberation of internal calcium (group I) or modulation of cAMP synthesis (groups II and III). Here we investigated the subtype of mGluR involved. Phosphorylation was strongly stimulated by the selective group II agonists DCG IV, L-CCG-I and 1S,3S-ACPD, whereas the group I agonist 3,5-DHPG and the group III agonist L-AP4 had no effect. These results show that the receptor regulating GFAP phosphorylation in the immature hippocampus has some of the properties of a group II mGluR.
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Affiliation(s)
- T Kommers
- Departmento de Bioquímica, ICBS, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
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2214
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Mu�oz A, Liu XB, Jones EG. Development of metabotropic glutamate receptors from trigeminal nuclei to barrel cortex in postnatal mouse. J Comp Neurol 1999. [DOI: 10.1002/(sici)1096-9861(19990712)409:4<549::aid-cne3>3.0.co;2-i] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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2215
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Colwell CS, Levine MS. Metabotropic glutamate receptor modulation of excitotoxicity in the neostriatum: role of calcium channels. Brain Res 1999; 833:234-41. [PMID: 10375699 DOI: 10.1016/s0006-8993(99)01545-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We have previously shown that metabotropic glutamate receptor (mGluR) activation can attenuate N-methyl-d-aspartate (NMDA)-induced excitotoxic injury in the neostriatum both in vivo and in vitro. Our earlier studies made use of the non-subtype selective mGluR agonist 1-amino-cyclopentane-1,3-dicarboxylic acid (tACPD). In the present study, we extended these observations by identifying the subtype of mGluR involved. Using selective mGluR agonists, we provide evidence that the Group II mGluRs are responsible for inhibition of NMDA excitotoxicity in the neostriatum. In addition, we provide evidence that the inhibitory effects of tACPD on excitotoxicity are dependent upon calcium influx as they are blocked by a low calcium solution as well as the broad-spectrum calcium channel blocker cadmium. The tACPD-induced attenuation was also blocked by omega-conotoxin GVIA suggesting participation of N-type calcium channels. Whole cell voltage clamp recordings were made to directly determine the effects of mGluRs on voltage-gated calcium channels in neostriatal neurons. As predicted, both tACPD and the Group II agonist 3C4HPG inhibited calcium currents in neostriatal neurons. Again this effect was blocked by omega-conotoxin GVIA. Overall the results suggest that mGluR regulation of voltage-gated calcium channels can limit NMDA toxicity in the neostriatum.
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Affiliation(s)
- C S Colwell
- Mental Retardation Research Center, Department of Psychiatry and Biobehavioral Sciences, University of California-Los Angeles, 760 Westwood Plaza, Los Angeles, CA 90024-1759, USA.
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2216
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Raymond V, Hamon A, Grau Y, Lapied B. DmGluRA, a Drosophila metabotropic glutamate receptor, activates G-protein inwardly rectifying potassium channels in Xenopus oocytes. Neurosci Lett 1999; 269:1-4. [PMID: 10821630 DOI: 10.1016/s0304-3940(99)00294-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Xenopus oocytes were coinjected with cDNAs encoding the Drosophila melanogaster metabotropic glutamate receptor (DmGluRA) and two mammalian G-protein inwardly rectifying potassium channel subunits (GIRK1 and GIRK2). Glutamate and two vertebrate group II mGluR agonists (order of potency: LY 354740 > glutamate > DCG IV) elicited inwardly rectifying potassium currents. These inward currents were sensitive to cesium and barium. They were also blocked by two group II specific antagonists MCCG and APICA (IC50s 97.5 and 200 microM, respectively) and not affected by a group I antagonist (AIDA). Finally, the A-protomer of PTX reduced the glutamate-induced GIRK currents. This study is the first characterization of an invertebrate mGluR-mediated GIRK currents via a PTX-sensitive G protein.
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Affiliation(s)
- V Raymond
- Laboratoire de Neurophysiologie, UPRES EA 2647, Université d'Angers, France
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2217
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Pizzi M, Boroni F, Bianchetti KM, Memo M, Spano P. Reversal of glutamate excitotoxicity by activation of PKC-associated metabotropic glutamate receptors in cerebellar granule cells relies on NR2C subunit expression. Eur J Neurosci 1999; 11:2489-96. [PMID: 10383638 DOI: 10.1046/j.1460-9568.1999.00669.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Stimulation of metabotropic glutamate receptors (mGluRs) belonging to group I has been found to reduce N-methyl-D-aspartate (NMDA) receptor function in terms of both intracellular calcium concentration ([Ca2+]i) rise and neurotoxicity in cultured cerebellar granule cells. In the present study, we investigated whether the mGluR-elicited modulation of glutamate responses might rely on the heteromeric composition of NMDA receptor channel. NMDA receptors consist of two distinct groups of subunits: NR1, that is ubiquitously in the receptor complexes; and NR2A-D, that differentiate and potentiate NMDA receptor responses by assembling with NR1. Among NR2 subunits, only NR2A and NR2C mRNAs and relative proteins are detected in cerebellar granule cells at 10 days in vitro. To dissect the involvement of the two different subunits in making the NMDA receptor channel sensitive to modulation by group I mGluR agonists, expression of the NR2C subunit was prevented by treating the cells with specific antisense oligodeoxynucleotide (ODN). The capability of the mGluR agonists, trans-1-amino-cyclopentane-1,3-dicarboxylic acid (tACPD, 100 microM) or 3 hydroxyphenylglycine (3HPG, 100 microM), and the protein kinase C (PKC) activator, 4beta-phorbol-12,13-dibutyrate (PDBu, 1 microM), to inhibit the function of resultant NMDA receptors was then evaluated. We found that depletion of the NR2C subunit abolished the inhibitory effect of group I mGluR stimulation on glutamate-induced [Ca2+]i rise and neurotoxicity. The antisense ODN treatment also prevented the inhibitory effect of PDBu on glutamate responses. Conversely, in NR2C-lacking neurons, both group I mGluRs and PKC stimulation enhanced NMDA receptor-mediated effects. The present findings indicate that the capability of PKC-associated mGluRs to modulate native NMDA receptor function relies on the heteromeric configuration of the receptor-channel complex. Particularly, expression of the NR2C subunit is required to make the NMDA receptor sensitive to inhibitory modulation by mGluRs or PKC activation.
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Affiliation(s)
- M Pizzi
- Division of Pharmacology, Department of Biomedical Sciences, School of Medicine, University of Brescia, Italy.
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2218
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Ishikawa K, Nash SR, Nishimune A, Neki A, Kaneko S, Nakanishi S. Competitive interaction of seven in absentia homolog-1A and Ca2+/calmodulin with the cytoplasmic tail of group 1 metabotropic glutamate receptors. Genes Cells 1999; 4:381-90. [PMID: 10469171 DOI: 10.1046/j.1365-2443.1999.00269.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Group 1 metabotropic glutamate receptors (mGluR1 and mGluR5) are coupled to inositol trisphosphate/Ca2+ signaling via G proteins and play an important role in excitatory synaptic transmission. To explore the regulation of group 1 mGluR function, we applied the yeast two-hybrid system using the intracellular carboxy-terminal domain of group 1 mGluRs (group 1 ct-mGluRs) and attempted to identify novel protein-protein interactions of group 1 mGluRs. RESULTS The two-hybrid screening revealed a specific interaction between group 1 ct-mGluRs and Siah-1A, the mammalian homolog of Drosophila seven in absentia which is involved in photoreceptor cell differentiation via the ubiquitin/proteasome-dependent mechanism. This interaction occurs within a homologous 27-28 amino acid stretch within group 1 ct-mGluRs and requires the latter two-thirds of Siah-1A. Following coexpression in COS-7 cells, myc-tagged Siah-1A was coimmunoprecipitated with the flag-tagged ct-mGluR1 by anti-flag antibody. Furthermore, in vitro binding revealed that Siah-1A and Ca2+/calmodulin (CaM) binding sites overlap, such that Siah-1A binding is competitively inhibited by CaM in a Ca2+-dependent manner. CONCLUSIONS The results demonstrate a direct interaction between group 1 mGluRs and Siah-1A and suggest a novel modulatory mechanism mediated by a competitive interaction between Ca2+/CaM and Siah-1A.
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Affiliation(s)
- K Ishikawa
- Department of Biological Sciences, Kyoto University Faculty of Medicine, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
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2219
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Neugebauer V, Chen PS, Willis WD. Role of metabotropic glutamate receptor subtype mGluR1 in brief nociception and central sensitization of primate STT cells. J Neurophysiol 1999; 82:272-82. [PMID: 10400956 DOI: 10.1152/jn.1999.82.1.272] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
G-protein coupled metabotropic glutamate receptors (mGluRs) are important modulators of synaptic transmission in the mammalian CNS and have been implicated in various forms of neuroplasticity and nervous system disorders. Increasing evidence also suggests an involvement of mGluRs in nociception and pain behavior although the contribution of individual mGluR subtypes is not yet clear. Subtypes mGluR1 and mGluR5 are classified as group I mGluRs and share the ability to stimulate phosphoinositide hydrolysis and activate protein kinase C. The present study examined the role of group I mGluRs in nociceptive processing and capsaicin-induced central sensitization of primate spinothalamic tract (STT) cells in vivo. In 10 anesthetized male monkeys (Macaca fascicularis) extracellular recordings were made from 20 STT cells in the lumbar dorsal horn. Responses to brief (15 s) cutaneous stimuli of innocuous (BRUSH) and barely and substantially noxious (PRESS and PINCH, respectively) intensity were recorded before, during, and after the infusion of group I mGluR agonists and antagonists into the dorsal horn by microdialysis. Cumulative concentration-response relationships were obtained by applying different concentrations for at least 20 min each (at 5 microl/min). The actual concentrations reached in the tissue are 2-3 orders of magnitude lower than those in the microdialysis fibers (values in this paper refer to the latter). The group I antagonists were also applied at 10-25 min after capsaicin injection. S-DHPG, a group I agonist at both mGluR1 and mGluR5, potentiated the responses to innocuous and noxious stimuli (BRUSH > PRESS > PINCH) at low concentrations (10-100 microM; n = 5) but had inhibitory effects at higher concentrations (1-10 mM; n = 5). The mGluR5 agonist CHPG (1 microM-100 mM; n = 5) did not potentiate but inhibited all responses (10-100 mM; n = 5). AIDA (1 microM-100 mM), a mGluR1-selective antagonist, dose-dependently depressed the responses to PINCH and PRESS but not to BRUSH (n = 6). The group I (mGluR1 > mGluR5) antagonist CPCCOEt (1 microM-100 mM) had similar effects (n = 6). Intradermal injections of capsaicin sensitized the STT cells to cutaneous mechanical stimuli. The enhancement of the responses by capsaicin resembled the potentiation by the group I mGluR agonist S-DHPG (BRUSH > PRESS > PINCH). CPCCOEt (1 mM) reversed the capsaicin-induced sensitization when given as posttreatment (n = 5). After washout of CPCCOEt, the sensitization resumed. Similarly, AIDA (1 mM; n = 7) reversed the capsaicin-induced sensitization and also blocked the potentiation by S-DHPG (n = 5). These data suggest that the mGluR1 subtype is activated endogenously during brief high-intensity cutaneous stimuli (PRESS, PINCH) and is critically involved in capsaicin-induced central sensitization.
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Affiliation(s)
- V Neugebauer
- Department of Anatomy and Neurosciences and Marine Biomedical Institute, The University of Texas Medical Branch, Galveston, Texas 77555-1069, USA
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2220
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Hodgson DM, Taylor AN, Zhang Z, Rosenberg A. Lysosphingomyelin prevents behavioral aberrations and hippocampal neuron loss induced by the metabotropic glutamate receptor agonist quisqualate. Prog Neuropsychopharmacol Biol Psychiatry 1999; 23:877-92. [PMID: 10509381 DOI: 10.1016/s0278-5846(99)00047-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. Excessive excitation of brain neurons by the excitatory neurotransmitter, glutamate, induces a cascade of events leading to increased intracellular Ca++, neuronal degeneration and death. 2. Recent in vitro research has demonstrated that a natural cationic amphiphile in the brain, lysosphingomyelin, may be able to prevent neuronal degeneration by repressing phosphosinositidase-C overactivation induced by excessive excitation of the metabotropic glutamate receptor. 3. This research tested the latter finding in vivo in a rat model of glutamate excitotoxicity. Intracerebroventricular (i.c.v.) administration of the Group 1 metabotropic glutamate receptor (mGluR) agonist, quisqualate, produced seizures, akinesia, destruction of hippocampal pyramidal cell dendritic microtubule-associated protein-2, and major loss of hippocampal CA sector neurons. 4. Prophylactic i.c.v. infusion of lysosphingomyelin powerfully attenuates these quisqualate-induced behaviors and prevents neuronal degeneration. 5. Lysosphingomyelin may be of clinical use in allaying progressive Group 1 mGluR-induced hippocampal cognitive and motor disorders including Alzheimer's disease, brain seizure, and stroke.
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Affiliation(s)
- D M Hodgson
- Dept. of Neurobiology, School of Medicine, University of California, Los Angeles, USA
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2221
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Salt TE, Binns KE, Turner JP, Gasparini F, Kuhn R. Antagonism of the mGlu5 agonist 2-chloro-5-hydroxyphenylglycine by the novel selective mGlu5 antagonist 6-methyl-2-(phenylethynyl)-pyridine (MPEP) in the thalamus. Br J Pharmacol 1999; 127:1057-9. [PMID: 10455248 PMCID: PMC1566135 DOI: 10.1038/sj.bjp.0702677] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Our previous work has shown that Group I mGlu receptors participate in thalamic sensory processing in vivo. However, unequivocal demonstration of mGlu5 participation has not been possible due to the lack of specific ligands. We have therefore made a preliminary study of the in vivo actions of the agonist (R,S)-2-Chloro-5-hydroxyphenylglycine [CHPG] and the novel mGlu5 antagonist 6-methyl-2-(phenylethynyl)-pyridine [MPEP] in order to characterize their suitability for functional studies. Iontophoretically administered MPEP selectively antagonized excitatory responses of single rat thalamic neurones to CHPG compared to the broad-spectrum mGlu agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate. In contrast, the established mGlu1 and mGlu5 antagonist (S)-4-carboxyphenylglycine reduced responses to both agonists. These findings are the first demonstration of an in vivo action of CHPG and its antagonism by a selective mGlu5 antagonist. Furthermore MPEP appears to be a good tool for functional studies of mGlu5.
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Affiliation(s)
- T E Salt
- Institute of Ophthalmology, University College London, UK.
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2222
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Abstract
Within a given family of seven transmembrane domain (7TM) receptors, functional diversity is most often afforded by the existence of multiple receptor subtypes, each encoded by a distinct gene. However, it is now clear that the existence of introns in genes encoding some members of a receptor family provides scope for additional diversity by virtue of splicing events that result in the formation of different receptor mRNAs and consequently distinct receptor isoforms. A large number of 7TM receptor splice variants have now been shown to exist. In this article, the current data on alternatively spliced variants for hormone and neurotransmitter 7TMs are reviewed, their potential physiological importance considered and some of the issues pertaining to the classification and nomenclature of receptor isoforms produced in this way are addressed.
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Affiliation(s)
- G J Kilpatrick
- Pre-clinical CNS Department, F. Hoffmann-La Roche, Basel 4070, Switzerland
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2223
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Beaver CJ, Ji Q, Daw NW. Effect of the group II metabotropic glutamate agonist, 2R,4R-APDC, varies with age, layer, and visual experience in the visual cortex. J Neurophysiol 1999; 82:86-93. [PMID: 10400937 DOI: 10.1152/jn.1999.82.1.86] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Group II metabotropic glutamate receptors (mGluR 2/3) are distributed differentially across the layers of cat visual cortex, and this distribution varies with age. At 3-4 wk, mGluR 2/3 receptor immunoreactivity is present in all layers. By 6-8 wk of age, it is still present in extragranular layers (2, 3, 5, and 6) but has disappeared from layer 4, and dark-rearing postpones the disappearance of Group II receptors from layer 4. We examined the physiological effects of Group II activation, to see if these effects varied similarly. The responses of single neurons in cat primary visual cortex were recorded to visual stimulation, then the effect of iontophoresis of 2R,4R-4 aminopyrrolidine-2, 4-decarboxylate (2R,4R-APDC), a Group II specific agonist, was observed in animals between 3 wk and adulthood. The effect of 2R, 4R-APDC was generally suppressive, reducing both the visual response and spontaneous activity of single neurons. The developmental changes were in agreement with the immunohistochemical results: 2R, 4R-APDC had effects on cells in all layers in animals of 3-4 wk but not in layer 4 of animals >6 wk old. Moreover, the effect of 2R, 4R-APDC was reduced in the cortex of older animals (>22 wk). Dark-rearing animals to 47-54 days maintained the effects of 2R, 4R-APDC in layer 4. The disappearance of Group II mGluRs from layer 4 between 3 and 6 wk of age is correlated with the segregation of ocular dominance columns in that layer, raising the possibility that mGluRs 2/3 are involved in this process.
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Affiliation(s)
- C J Beaver
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, Connecticut 06520-8061, USA
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2224
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Pin JP, De Colle C, Bessis AS, Acher F. New perspectives for the development of selective metabotropic glutamate receptor ligands. Eur J Pharmacol 1999; 375:277-94. [PMID: 10443583 DOI: 10.1016/s0014-2999(99)00258-7] [Citation(s) in RCA: 119] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The metabotropic glutamate receptors are GTP-binding-protein (G-protein) coupled receptors that play important roles in regulating the activity of many synapses in the central nervous system. As such, these receptors are involved in a wide number of physiological and pathological processes. Within the last few years, new potent and selective agonists and antagonists as well as radioligands acting on these receptors have been developed. Molecular modeling studies revealed the structural features of the glutamate binding site, and will be useful for the design of more selective and potent ligands. More interestingly, recent data revealed new regulatory sites on the receptor protein, able either to decrease or potentiate the action of the endogenous ligand. No doubt that in the near future a multitude of new tools to modulate the activity of these receptors will be discovered, enabling the identification of the possible therapeutic applications for these new neuroactive molecules.
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Affiliation(s)
- J P Pin
- Centre INSERM-CNRS de Pharmacologie-Endocrinologie, UPR 9023-CNRS, Laboratoire des Mécanismes Moléculaires des Communications Cellulaires, Montpellier, France.
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2225
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Bräuner-Osborne H, Jensen AA, Sheppard PO, O'Hara P, Krogsgaard-Larsen P. The agonist-binding domain of the calcium-sensing receptor is located at the amino-terminal domain. J Biol Chem 1999; 274:18382-6. [PMID: 10373443 DOI: 10.1074/jbc.274.26.18382] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The calcium-sensing receptor (CaR) is a G-protein-coupled receptor that displays 19-25% sequence identity to the gamma-aminobutyric acid type B (GABAB) and metabotropic glutamate (mGlu) receptors. All three groups of receptors have a large amino-terminal domain (ATD), which for the mGlu receptors has been shown to bind the endogenous agonist. To investigate whether the agonist-binding domain of the CaR also is located in the ATD, we constructed a chimeric receptor named Ca/1a consisting of the ATD of CaR and the seven transmembrane region and C terminus of mGlu1a. The Ca/1a receptor stimulated inositol phosphate production when exposed to the cationic agonists Ca2+, Mg2+, and Ba2+ in transiently transfected tsA cells (a transformed HEK 293 cell line). The pharmacological profile of Ca/1a (EC50 values of 3.3, 2.6, and 3.9 mM for these cations, respectively) was very similar to that of the wild-type CaR (EC50 values of 3.2, 4.7, and 4.1 mM, respectively). For the mGlu1a receptor, it has been shown that Ser-165 and Thr-188, which are located in the ATD, are involved in the agonist binding. An alignment of CaR with the mGlu receptors showed that these two amino acid residues have been conserved in CaR as Ser-147 and Ser-170, respectively. Each of these residues was mutated to alanines and tested pharmacologically using the endogenous agonist Ca2+. CaR-S147A showed an impaired function as compared with wild-type CaR both with respect to potency of Ca2+ (4-fold increase in EC50) and maximal response (79% of wild-type response). CaR-S170A showed no significant response to Ca2+ even at 50 mM concentration. In contrast, each of the two adjacent mutations, S169A and S171A, resulted in pharmacological profiles almost identical to that of the wild-type receptor. These data demonstrate that Ser-170 and to some extent Ser-147 are involved in the Ca2+ activation of the CaR, and taken together, our results reveal a close resemblance of the activation mechanism between the CaR and the mGlu receptors.
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Affiliation(s)
- H Bräuner-Osborne
- Department of Medicinal Chemistry, NeuroScience PharmaBiotec Research Centre, The Royal Danish School of Pharmacy, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.
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2226
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Kleinlogel S, Oestreicher E, Arnold T, Ehrenberger K, Felix D. Metabotropic glutamate receptors group I are involved in cochlear neurotransmission. Neuroreport 1999; 10:1879-82. [PMID: 10501525 DOI: 10.1097/00001756-199906230-00015] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
All three types of ionotropic glutamate receptors, AMPA, NMDA and kainate, contribute to the neurotransmission between inner hair cells (IHC) and afferent neurons in the mammalian cochlea. We used microiontophoretic techniques to investigate whether metabotropic glutamate receptors group I (mGluR I) are also involved in the transmission of IHC afferents of the guinea pig. The mGluR I agonist DHPG produced an increase in afferent firing, which lasted significantly longer than that of the ionotropic agonists AMPA and NMDA. The activation was reversibly blocked by the mGluR I antagonist AIDA in a dose-dependent manner. AIDA also diminished spontaneous activity, but only slightly affected the AMPA- or NMDA-induced firing rate. Our results suggest that mGluR I are involved in peripheral auditory processing.
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Affiliation(s)
- S Kleinlogel
- Division of Neurobiology, University of Berne, Switzerland
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2227
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Kozikowski AP, Araldi GL, Tückmantel W, Pshenichkin S, Surina E, Wroblewski JT. 1-amino-APDC, a partial agonist of group II metabotropic glutamate receptors with neuroprotective properties. Bioorg Med Chem Lett 1999; 9:1721-6. [PMID: 10397508 DOI: 10.1016/s0960-894x(99)00266-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The synthesis of the 1-amino derivative of (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylic acid (1-amino-APDC), a selective metabotropic glutamate ligand, is disclosed. This compound acts as a partial agonist of the group II mGluRs and shows pronounced neuroprotective properties in the NMDA model of cell toxicity.
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Affiliation(s)
- A P Kozikowski
- Georgetown University Medical Center, Drug Discovery Laboratory, Institute for Cognitive & Computational Sciences, Washington, DC 20007-2197, USA
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2228
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Relationships between the prefrontal cortex and the basal ganglia in the rat: physiology of the cortico-nigral circuits. J Neurosci 1999. [PMID: 10341265 DOI: 10.1523/jneurosci.19-11-04674.1999] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The prelimbic/medial orbital areas (PL/MO) of the rat prefrontal cortex are connected to substantia nigra pars reticulata (SNR) through three main circuits: a direct nucleus accumbens (NAcc)-SNR pathway, an indirect NAcc-SNR pathway involving the ventral pallidum (VP) and the subthalamic nucleus (STN), and a disynaptic cortico-STN-SNR pathway. The present study was undertaken to characterize the effect of PL/MO stimulation on SNR cells and to determine the contribution of these different pathways. The major pattern of responses observed in the SNR was an inhibition preceded by an early excitation and followed or not by a late excitation. The inhibition resulted from the activation of the direct NAcc-SNR pathway because it disappeared after acute blockade of the glutamatergic cortico-striatal transmission by CNQX application into the NAcc. The late excitation resulted from the activation of the indirect NAcc-VP-STN-SNR pathway via a disinhibition of the STN because it disappeared after either CNQX application into the NAcc or blockade of the GABAergic striato-pallidal transmission by bicuculline application into the VP. The early excitation, which was markedly decreased after blockade of the cortico-STN transmission by CNQX application into the STN, resulted from the activation of the disynaptic cortico-STN-SNR pathway. Finally, the blockade of the cortico-STN-VP circuit by CNQX application into STN or VP modified the influence of the trans-striatal circuits on SNR cells. This study suggests that, in the prefrontal cortex-basal ganglia circuits, the trans-subthalamic pathways, by their excitatory effects, participate in the shaping of the inhibitory influence of the direct striato-nigral pathway on SNR neurons.
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2229
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Ferraguti F, Baldani-Guerra B, Corsi M, Nakanishi S, Corti C. Activation of the extracellular signal-regulated kinase 2 by metabotropic glutamate receptors. Eur J Neurosci 1999; 11:2073-2082. [PMID: 10336676 DOI: 10.1046/j.1460-9568.1999.00626.x] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Activation of metabotropic glutamate receptors (mGluRs) leads to modulation of a variety of second messenger pathways probably including the mitogen-activated protein kinase (MAPK) extracellular signal-regulated protein kinases (ERK). MAPK play a key role in the control of cellular responses to changes in the external environment by regulating transcriptional activity and the phosphorylation state of several cytoplasmic targets. In this study, Chinese hamster ovary (CHO) cells permanently transfected with rat mGluR1a, mGluR2 and mGluR4 were employed as a model to examine the activation of MAPK by glutamate through mGluRs. All three mGluR subtypes rapidly stimulated ERK activation. In particular, mGluR1a and mGluR2 preferentially mediated phosphorylation and activation of ERK2 in a pertussis toxin (PTX)-sensitive and concentration-dependent manner. The activation was blocked completely by pretreatment with the antagonist (rs)-alpha-methyl-4-carboxyphenylglycine (MCPG) or with the MEK inhibitor PD098059. Furthermore, mGluR1a-mediated ERK activation was suppressed by the depletion of endogenous protein kinase C (PKC) activity and by the PKC inhibitors staurosporine and calphostin C, but not chelerythrine. When cAMP was elevated in mGluR2-expressing cells, by forskolin or dibutyryl-cAMP, slight elevation of ERK activity was observed. However, glutamate-stimulated ERK activation remained unaffected. In these cells, the phosphatidylinositol 3 kinase (PI3K) inhibitor wortmannin produced a significant, albeit only partial, inhibition of mGluR2-mediated ERK activation. These findings raise the possibility of a MAPK cascade involvement in glutamate-dependent neuronal plasticity mediated through stimulation of mGluRs.
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Affiliation(s)
- F Ferraguti
- GlaxoWellcome Medicine Research Centre, Verona, Italy.
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2230
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2231
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Bortolotto ZA, Fitzjohn SM, Collingridge GL. Roles of metabotropic glutamate receptors in LTP and LTD in the hippocampus. Curr Opin Neurobiol 1999; 9:299-304. [PMID: 10395580 DOI: 10.1016/s0959-4388(99)80044-0] [Citation(s) in RCA: 159] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Metabotropic L-glutamate receptors are involved in various forms of synaptic plasticity in the hippocampus. The use of a new antagonist (LY341495) that blocks all known metabotropic L-glutamate receptors in the brain, together with subtype-selective antagonists, has identified multiple roles both for cloned and novel metabotropic L-glutamate receptors in hippocampal long-term potentiation and long-term depression.
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Affiliation(s)
- Z A Bortolotto
- Department of Anatomy, MRC Centre for Synaptic Plasticity, University of Bristol School of Medical Sciences, University Walk, Bristol, BS8 1TD, UK.
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2232
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Mitsikostas DD, Sanchez del Rio M, Waeber C, Huang Z, Cutrer FM, Moskowitz MA. Non-NMDA glutamate receptors modulate capsaicin induced c-fos expression within trigeminal nucleus caudalis. Br J Pharmacol 1999; 127:623-30. [PMID: 10401552 PMCID: PMC1566054 DOI: 10.1038/sj.bjp.0702584] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. We examined the effects of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzol[f]quinoxaline-7-sulpho namide (NBQX), the kainate receptor antagonists gamma-(R-)-glutamylaminomethanesulphonic acid (GAMS) and 6,7,8,9-tetrahydro-5-nitro-1H-benz[g]indole-2,3-dione-3-oxime (NS-102), and the group III metabotropic glutamate receptor (mGluR) agonist 2-amino-4-phosphono-S-butanoic acid (L-AP4) on c-fos-like immunoreactivity (c-fos LI) in trigeminal caudalis (Sp5C), lateral reticular (LRt), medullary reticular (Md) and solitary tract (Sol) nuclei, after intracisternal injection of capsaicin in urethane anaesthetized Sprague-Dawley rats. 2. Few c-fos labelled cells were observed within Sp5C in capsaicin-vehicle treated animals. The number of positive c-fos cells increased by 17 fold after intracisternal capsaicin (5 nmol) administration. 3. Pretreatment with CNQX (0.02, 0.1, 0.6, 3 and 15 mg kg-1) or NBQX (0.01, 0.1 and 1 mg kg-1), administered intraperitoneally 15 min before capsaicin, significantly reduced labelled cells within Sp5C by a maximum of 45 and 34%, respectively. The number of c-fox LI cells within LRt, Md and Sol was not affected. Pretreatment with L-AP4 (1, 3 and 10 mg kg-1) decreased the number of Sp5C c-fos LI cells by a maximum of 30%, whereas GAMS (1 and 10 mg kg-1) and NS-102 (1 and 5 mg kg-1) did not show any significant effect. 4. These results suggest that blockade of AMPA receptors, but not kainate receptors, or the activation of group III mGluRs, decrease the response of Sp5C neurons to trigeminovascular activation. Thus, in addition to NMDA receptors, mGluRs and AMPA receptors may modulate cephalic pain and may provide a potential therapeutic target for antimigraine drugs.
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Affiliation(s)
- Dimos D Mitsikostas
- Stroke & Neurovascular Regulation Laboratory, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Boston, Massachusetts, MA 02129, U.S.A
| | - Margarita Sanchez del Rio
- Stroke & Neurovascular Regulation Laboratory, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Boston, Massachusetts, MA 02129, U.S.A
| | - Christian Waeber
- Stroke & Neurovascular Regulation Laboratory, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Boston, Massachusetts, MA 02129, U.S.A
| | - Zhihong Huang
- Stroke & Neurovascular Regulation Laboratory, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Boston, Massachusetts, MA 02129, U.S.A
| | - F Michael Cutrer
- Stroke & Neurovascular Regulation Laboratory, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Boston, Massachusetts, MA 02129, U.S.A
| | - Michael A Moskowitz
- Stroke & Neurovascular Regulation Laboratory, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Boston, Massachusetts, MA 02129, U.S.A
- Author for correspondence:
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2233
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Vetter P, Garthwaite J, Batchelor AM. Regulation of synaptic transmission in the mossy fibre-granule cell pathway of rat cerebellum by metabotropic glutamate receptors. Neuropharmacology 1999; 38:805-15. [PMID: 10465684 DOI: 10.1016/s0028-3908(99)00003-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The role of metabotropic glutamate receptors (mGluRs) in the mossy fibre-granule cell pathway in rat cerebellum was studied using slice preparations and electrophysiological techniques. Application of the group I selective agonist (S)-3,5-dihydroxyphenylglycine (DHPG) evoked, in a concentration-dependent manner (EC50 = 33 microM), a depolarising/hyperpolarising complex response from granule cells which was preferentially inhibited by the group I selective antagonist (S)-4-carboxyphenylglycine (4CPG). The group III selective agonist L-amino-4-phosphonobutyrate (AP4) evoked a hyperpolarising response (EC50 = 10 microM) which was inhibited by the group II/III selective antagonist (S)-alpha-methyl-4-phosphonophenylglycine (MPPG). The group II agonist (2S,2'R,3'R)-2-(2',3'-dicarboxylcyclopropyl)glycine (DCG-IV) elicited no measurable voltage change. The amplitude of the synaptically-mediated mossy fibre response in granule cells was unaffected during application of AP4, was reduced by DHPG and was enhanced by DCG-IV (EC50 = 80 nM). These effects were inhibited by the group selective antagonists 4CPG and (2S,1'S,2'S,3'R)-2-(2'-carboxy-3'-phenylcyclopropyl)glycine (PCCG-4), respectively. Further investigation using patch-clamp recording revealed that DCG-IV potently inhibited spontaneous GABAergic currents. We conclude that group I and III (but not group II) mGluRs are functionally expressed by granule cells, whereas unexpectedly group II or III mGluRs do not appear to be present presynaptically on mossy fibre terminals. Group II mGluRs are located on Golgi cell terminals; when activated these receptors cause disinhibition, a function which may be important for gating information transfer from the mossy fibres to the granule cells.
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Affiliation(s)
- P Vetter
- The Wolfson Institute for Biomedical Research, University College London, UK
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2234
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Dauban P, de Saint-Fuscien C, Dodd RH. Application of 2,3-aziridino-γ-lactone methodology toward the enantiospecific synthesis of the (3S,4S)-isomer of dihydroxy-L-glutamic acid. Tetrahedron 1999. [DOI: 10.1016/s0040-4020(99)00405-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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2235
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Saransaari P, Oja SS. Involvement of metabotropic glutamate receptors in taurine release in the adult and developing mouse hippocampus. Amino Acids 1999; 16:165-79. [PMID: 10319187 DOI: 10.1007/bf01321534] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The inhibitory amino acid taurine has been held to function as an osmoregulator and modulator of neural activity, being particularly important in the immature brain. Ionotropic glutamate receptor agonists are known markedly to potentiate taurine release. The effects of different metabotropic glutamate receptor (mGluR) agonists and antagonists on the basal and K(+)-stimulated release of [3H]taurine from hippocampal slices from 3-month-old (adult) and 7-day-old mice were now investigated using a superfusion system. Of group I metabotropic glutamate receptor agonists, quisqualate potentiated basal taurine release in both age groups, more markedly in the immature hippocampus. This action was not antagonized by the specific antagonists of group I but by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione (NBQX), which would suggest an involvement of ionotropic glutamate receptors. (S)-3,5-dihydroxyphenylglycine (DHPG) potentiated the basal release by a receptor-mediated mechanism in the immature hippocampus. The group II agonist (2S, 2'R, 3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG IV) markedly potentiated basal taurine release at both ages. These effects were antagonized by dizocilpine, indicating again the participation of ionotropic receptors. Group III agonists slightly potentiated basal taurine release, as did several antagonists of the three metabotropic receptor groups. Potassium-stimulated (50 mM K+) taurine release was generally significantly reduced by mGluR agents, mainly by group I and II compounds. This may be harmful to neurons in hyperexcitatory states. On the other hand, the potentiation by mGluRs of basal taurine release, particularly in the immature hippocampus, together with the earlier demonstrated pronounced enhancement by activation of ionotropic glutamate receptors, may protect neurons against excitotoxicity.
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Affiliation(s)
- P Saransaari
- Tampere Brain Research Center, University of Tampere Medical School, Finland.
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2236
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Galvez T, Parmentier ML, Joly C, Malitschek B, Kaupmann K, Kuhn R, Bittiger H, Froestl W, Bettler B, Pin JP. Mutagenesis and modeling of the GABAB receptor extracellular domain support a venus flytrap mechanism for ligand binding. J Biol Chem 1999; 274:13362-9. [PMID: 10224098 DOI: 10.1074/jbc.274.19.13362] [Citation(s) in RCA: 172] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The gamma-aminobutyric acid type B (GABAB) receptor is distantly related to the metabotropic glutamate receptor-like family of G-protein-coupled receptors (family 3). Sequence comparison revealed that, like metabotropic glutamate receptors, the extracellular domain of the two GABAB receptor splice variants possesses an identical region homologous to the bacterial periplasmic leucine-binding protein (LBP), but lacks the cysteine-rich region common to all other family 3 receptors. A three-dimensional model of the LBP-like domain of the GABAB receptor was constructed based on the known structure of LBP. This model predicts that four of the five cysteine residues found in this GABAB receptor domain are important for its correct folding. This conclusion is supported by analysis of mutations of these Cys residues and a decrease in the thermostability of the binding site after dithiothreitol treatment. Additionally, Ser-246 was found to be critical for CGP64213 binding. Interestingly, this residue aligns with Ser-79 of LBP, which forms a hydrogen bond with the ligand. The mutation of Ser-269 was found to differently affect the affinity of various ligands, indicating that this residue is involved in the selectivity of recognition of GABAB receptor ligands. Finally, the mutation of two residues, Ser-247 and Gln-312, was found to increase the affinity for agonists and to decrease the affinity for antagonists. Such an effect of point mutations can be explained by the Venus flytrap model for receptor activation. This model proposes that the initial step in the activation of the receptor by agonist results from the closure of the two lobes of the binding domain.
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Affiliation(s)
- T Galvez
- Centre INSERM-CNRS de Pharmacologie-Endocrinologie, Mécanismes Moléculaires des Communications Cellulaires, CNRS UPR 9023, 141 rue de la Cardonille, 34094 Montpellier Cedex 5, France
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2237
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Barritt LC, Fritzsch B, Beisel KW. Characterization of G-protein betagamma expression in inner ear. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1999; 68:42-54. [PMID: 10320782 DOI: 10.1016/s0169-328x(99)00078-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Heterotrimeric guanine nucleotide binding proteins (G-proteins) are composed of a diverse set of alpha, beta, and gamma subunits, which couple cell surface receptors to intracellular effectors, such as adenylyl cyclase, phospholipase Cbeta, and ion channels. Both the Galpha and the Gbetagamma dimers mediate effector activity and are believed to contribute to the complexity of the signaling pathway. Molecular and immunocytochemical techniques were employed to determine diversity of Gbeta and Ggamma subunit expression in the murine inner ear. PCR-based assessment of lambdaZAP unidirectional cDNA libraries, representing the cochlea and inner ear hair cells, indicated all five known Gbeta subunits were present in the cochlea, while only a subset of Ggamma isoforms were found. New or novel G-protein beta and gamma subunits were not detected. cDNAs representing Gbeta1-4 and Ggamma2, Ggamma3, Ggamma5, Ggamma8olf subunit transcripts were isolated. In addition, cDNAs corresponding to the Gbeta5 and Ggamma11 isoforms exhibited restricted expression to inner and outer hair cells, respectively. Antisera specific for Gbeta3, Gbeta4, Ggamma3, Ggamma5 and Ggamma11 stained spiral ganglion and neurosensory hair cells. A unique finding was the variable topological distribution of Ggamma3 in the spiral ganglion cells along the cochlear axis. Collectively, our results demonstrate a complementary as well as differential distribution pattern for Gbeta and Ggamma isoforms exists in the inner ear. The co-localization of various G-protein isoforms within the same cell type suggests specific combinatorial Gbeta and Ggamma subunit associations may preferentially be formed. Thus, the detection of multiple subunits presumably reflects the extent of the functional diversity of inner ear signaling pathways and should provide specificity of G-protein mediated pathways.
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Affiliation(s)
- L C Barritt
- Center for Hereditary Communication Disorders, Boys Town National Research Hospital, Omaha, NE 68131, USA
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2238
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Keele NB, Neugebauer V, Shinnick-Gallagher P. Differential effects of metabotropic glutamate receptor antagonists on bursting activity in the amygdala. J Neurophysiol 1999; 81:2056-65. [PMID: 10322047 DOI: 10.1152/jn.1999.81.5.2056] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Differential effects of metabotropic glutamate receptor antagonists on bursting activity in the amygdala. Metabotropic glutamate receptors (mGluRs) are implicated in both the activation and inhibition of epileptiform bursting activity in seizure models. We examined the role of mGluR agonists and antagonists on bursting in vitro with whole cell recordings from neurons in the basolateral amygdala (BLA) of amygdala-kindled rats. The broad-spectrum mGluR agonist 1S,3R-1-aminocyclopentane dicarboxylate (1S,3R-ACPD, 100 microM) and the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG, 20 microM) evoked bursting in BLA neurons from amygdala-kindled rats but not in control neurons. Neither the group II agonist (2S,3S,4S)-alpha-(carboxycyclopropyl)-glycine (L-CCG-I, 10 microM) nor the group III agonist L-2-amino-4-phosphonobutyrate (L-AP4, 100 microM) evoked bursting. The agonist-induced bursting was inhibited by the mGluR1 antagonists (+)-alpha-methyl-4-carboxyphenylglycine [(+)-MCPG, 500 microM] and (S)-4-carboxy-3-hydroxyphenylglycine [(S)-4C3HPG, 300 microM]. Kindling enhanced synaptic strength from the lateral amygdala (LA) to the BLA, resulting in synaptically driven bursts at low stimulus intensity. Bursting was abolished by (S)-4C3HPG. Further increasing stimulus intensity in the presence of (S)-4C3HPG (300 microM) evoked action potential firing similar to control neurons but did not induce epileptiform bursting. In kindled rats, the same threshold stimulation that evoked epileptiform bursting in the absence of drugs elicited excitatory postsynaptic potentials in (S)-4C3HPG. In contrast (+)-MCPG had no effect on afferent-evoked bursting in kindled neurons. Because (+)-MCPG is a mGluR2 antagonist, whereas (S)-4C3HPG is a mGluR2 agonist, the different effects of these compounds suggest that mGluR2 activation decreases excitability. Together these data suggest that group I mGluRs may facilitate and group II mGluRs may attenuate epileptiform bursting observed in kindled rats. The mixed agonist-antagonist (S)-4C3HPG restored synaptic transmission to control levels at the LA-BLA synapse in kindled animals. The different actions of (S)-4C3HPG and (+)-MCPG on LA-evoked bursting suggests that the mGluR1 antagonist-mGluR2 agonist properties may be the distinctive pharmacology necessary for future anticonvulsant compounds.
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Affiliation(s)
- N B Keele
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas 77555-1031, USA
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2239
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Bongianni F, Deliagina TG, Grillner S. Role of glutamate receptor subtypes in the lamprey respiratory network. Brain Res 1999; 826:298-302. [PMID: 10224308 DOI: 10.1016/s0006-8993(99)01251-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The respiratory role of glutamate receptors was investigated in the isolated lamprey brain preparation by analyzing the changes in respiratory activity induced by bath application of specific antagonists of ionotropic and metabotropic glutamate receptors. The results show that these antagonists differentially affect the pattern of breathing and provide the first evidence that both ionotropic and metabotropic glutamate receptors are involved in neurotransmission within the lamprey respiratory network.
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Affiliation(s)
- F Bongianni
- Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, 17177, Stockholm, Sweden.
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2240
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Foley CM, Vogl HW, Mueller PJ, Hay M, Hasser EM. Cardiovascular response to group I metabotropic glutamate receptor activation in NTS. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:R1469-78. [PMID: 10233041 DOI: 10.1152/ajpregu.1999.276.5.r1469] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Glutamate is the proposed neurotransmitter of baroreceptor afferents at the level of the nucleus tractus solitarius (NTS). Exogenous glutamate in the NTS activates neurons through ionotropic and metabotropic glutamate receptors (mGluRs). This study tested the hypothesis that group I mGluRs in the NTS produce depressor, bradycardic, and sympathoinhibitory responses. In urethan-anesthetized rats, unilateral 30-nl microinjections of the group I-selective mGluR agonist 3,5-dihydroxyphenylglycine (DHPG) into the NTS decreased mean arterial pressure, heart rate, and lumbar sympathetic nerve activity. The dose of drug that produced 50% of the maximal response (ED50) was 50-100 microM. The response to microinjection of equal concentrations of DHPG or the general mGluR agonist 1-aminocyclopentane-1S,3R-dicarboxylic acid (ACPD) produced similar cardiovascular effects. The cardiovascular response to injection of DHPG or ACPD was abolished by NTS blockade of mGluRs with alpha-methyl-4-carboxyphenylglycine (MCPG). Blockade of ionotropic glutamate receptors with kynurenic acid did not attenuate the response to DHPG or ACPD injection. These data suggest that DHPG and ACPD activate mGluRs in the NTS and do not require ionotropic glutamate receptors to produce their cardiovascular response. In the NTS the group I mGluRs produce responses that are consistent with excitation of neurons involved in reducing sympathetic outflow, heart rate, and arterial pressure.
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Affiliation(s)
- C M Foley
- Department of Veterinary Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, Missouri 65211, USA
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2241
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Macek TA, Schaffhauser H, Conn PJ. Activation of PKC disrupts presynaptic inhibition by group II and group III metabotropic glutamate receptors and uncouples the receptor from GTP-binding proteins. Ann N Y Acad Sci 1999; 868:554-7. [PMID: 10414335 DOI: 10.1111/j.1749-6632.1999.tb11327.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- T A Macek
- Program in Molecular Therapeutics and Toxicology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
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2242
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Alagarsamy S, Rouse ST, Gereau RW, Heinemann SF, Smith Y, Conn PJ. Activation of N-methyl-D-aspartate receptors reverses desensitization of metabotropic glutamate receptor, mGluR5, in native and recombinant systems. Ann N Y Acad Sci 1999; 868:526-30. [PMID: 10414329 DOI: 10.1111/j.1749-6632.1999.tb11321.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- S Alagarsamy
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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2243
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Bradley SR, Standaert DG, Levey AI, Conn PJ. Distribution of group III mGluRs in rat basal ganglia with subtype-specific antibodies. Ann N Y Acad Sci 1999; 868:531-4. [PMID: 10414330 DOI: 10.1111/j.1749-6632.1999.tb11322.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- S R Bradley
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
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2244
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Bradley SR, Standaert DG, Rhodes KJ, Rees HD, Testa CM, Levey AI, Conn PJ. Immunohistochemical localization of subtype 4a metabotropic glutamate receptors in the rat and mouse basal ganglia. J Comp Neurol 1999. [DOI: 10.1002/(sici)1096-9861(19990428)407:1<33::aid-cne3>3.0.co;2-g] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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2245
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Malherbe P, Kratzeisen C, Lundstrom K, Richards JG, Faull RL, Mutel V. Cloning and functional expression of alternative spliced variants of the human metabotropic glutamate receptor 8. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1999; 67:201-10. [PMID: 10216218 DOI: 10.1016/s0169-328x(99)00050-9] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Two new spliced variants of the human metabotropic glutamate receptor 8 (HmGluR8), designated HmGluR8b and HmGluR8c, were identified in a human fetal brain cDNA library. The HmGluR8b and c differ from previously reported HmGluR8a by the out-of-frame insertions of 55-bp and 74-bp, respectively. The 55-bp insertion which contains a stop codon resulted in substitution of the last 16 amino acids in the C-terminus of HmGluR8a with 16 different amino acids in HmGluR8b. The 74-bp insertion introduces a frame shift in the predicted translation resulting in termination of the polypeptide before the putative seven transmembrane domains. Thus, the predicted HmGluR8c protein is 501 amino acids long and could represent a secreted isoform of the receptor. The pattern of mRNA expression of mGluR8 variants in human brain were analyzed by RT-PCR, Northern blot and in situ hybridization. Both HmGluR8a and b are expressed with similar abundance in fetal and adult brains. The in situ hybridization results indicate a predominantly glial cell expression of HmGluR8c in human brain. The three isoforms were transiently expressed in CHO cells from Semliki Forest Virus vectors. [3H]l-AP4 binding was performed on the cell membranes and the saturation curves showed the presence of a binding site with KD values of 249 and 182 nM and Bmax values of 13.6 and 10.5 pmoles/mg protein for HmGluR8a and b, respectively. For the six mGluR ligands studied, a similar rank order of potency was observed on both HmGluRa and b: l-AP4>l-SOP=l-CCG I>l-glutamate>DCG IV>LY 354740.
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Affiliation(s)
- P Malherbe
- Pharma Division PRPN, Bldg. 69/333, Preclinical CNS Research, F. Hoffmann-La Roche, CH-4070, Basel, Switzerland.
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2246
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Han G, Hampson DR. Ligand binding to the amino-terminal domain of the mGluR4 subtype of metabotropic glutamate receptor. J Biol Chem 1999; 274:10008-13. [PMID: 10187777 DOI: 10.1074/jbc.274.15.10008] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The metabotropic glutamate receptor (mGluR) 4 subtype of metabotropic glutamate receptor is a presynaptic receptor that modulates neurotransmitter release. We have characterized the properties of a truncated, epitope-tagged construct containing part of the extracellular amino-terminal domain of mGluR4. The truncated receptor was secreted into the cell culture medium of transfected human embryonic kidney cells. The oligomeric structure of the soluble truncated receptor was assessed by gel electrophoresis. In the presence of high concentrations of a reducing agent, the truncated receptor migrated as a monomer; at lower concentrations of the reducing agent, only higher molecular weight oligomers were observed. Competition binding experiments using the radiolabeled agonist [3H]L-2-amino-4-phosphonobutyric acid revealed that the rank order of potency of metabotropic ligands at the truncated receptor was similar to that of the full-length membrane-bound receptor. However, the truncated receptor displayed higher affinities for agonists and lower affinities for antagonists compared with the full-length receptor. Deglycosylation produced a shift in the relative molecular weight of the soluble protein from Mr = 71,000 to Mr = 63,000; deglycosylation had no effect on the binding of [3H]L-2-amino-4-phosphonobutyric acid, indicating that the asparagine-linked carbohydrates are not necessary for agonist binding. These results demonstrate that although the primary determinants of ligand binding to mGluR4 are contained within the first 548 amino acids of the receptor, additional amino acids located downstream of this region may influence the affinity of ligands for the binding site.
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Affiliation(s)
- G Han
- Faculty of Pharmacy and Department of Pharmacology University of Toronto, Toronto, Ontario M5S 252, Canada
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2247
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Yoshikawa T, Sugawara T, Hirano K, Stella VJ. A novel chemical delivery system for brain targeting. Adv Drug Deliv Rev 1999; 36:255-275. [PMID: 10837719 DOI: 10.1016/s0169-409x(98)00091-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Two different chemical approaches for brain drug delivery and targeting are proposed in the present review. One is a chemical drug delivery using a ring-closure reaction to the hydrophilic quaternary thiazolium compound in the brain. The other is a chemical drug targeting utilizing the nutrient receptor (transporter) system on the blood-brain barrier. The brain delivery system has been optimized and it was demonstrated that the brain delivery of three drugs, a drug for Parkinson's disease, an excitatory amino acid antagonist and a free radical scavenger, were improved by the conjugation with cis-2-formylaminoethenylthio derivatives in vivo. As for the brain targeting system, it was demonstrated that the conjugation with L-Glu improved the drug's brain distribution via the L-Glu excitatory and/or transport receptors in vitro and in vivo. These findings suggest that the concepts of two chemical approaches will contribute to the development of new central nervous system drugs.
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Affiliation(s)
- T Yoshikawa
- Shionogi Research Laboratories, Shionogi & Co. Ltd., Osaka 553-0002, Japan
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2248
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Servitja JM, Masgrau R, Sarri E, Picatoste F. Group I metabotropic glutamate receptors mediate phospholipase D stimulation in rat cultured astrocytes. J Neurochem 1999; 72:1441-7. [PMID: 10098847 DOI: 10.1046/j.1471-4159.1999.721441.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have studied the activation of phospholipase D (PLD) by glutamate in rat cultured astrocytes by measuring the PLD-catalyzed formation of [32P]phosphatidylbutanol in [32P]Pi-prelabeled cells, stimulated in the presence of butanol. Glutamate elicited the activation of PLD in cortical astrocytes but not in cortical neurons, whereas similar glutamate activation of phosphoinositide phospholipase C was found in both astrocytes and neurons. The extent of PLD stimulation by glutamate was similar in astrocytes from brain cortex and hippocampus, but no effect was found in cerebellar astrocytes. In cortical astrocytes, the glutamate response was insensitive to antagonists of ionotropic glutamate receptors and was reproduced by agonists of metabotropic glutamate receptors (mGluRs) with a rank order of agonist potency similar to that reported for group I mGluR-mediated phosphoinositide phospholipase activation [quisqualate > (S)-3,5-dihydroxyphenylglycine > (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid]. The response to (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid was inhibited by the mGluR antagonist (S)-alpha-methyl-4-carboxyphenylglycine and, less potently, by 1-aminoindan-1,5-dicarboxylic acid and 4-carboxyphenylglycine, two antagonists of group I mGluRs that display higher potency on mGluR1 than on mGluR5. The mGluR5-selective agonist (RS)-2-chloro-5-hydroxyphenylglycine also activated PLD in astrocytes. These findings indicate the involvement of group I mGluRs, most likely mGluR5, in the glutamate activation of PLD in cultured rat cortical astrocytes.
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Affiliation(s)
- J M Servitja
- Departament de Bioquímica i Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Bellaterra, Catalonia, Spain
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2249
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Kammermeier PJ, Ikeda SR. Expression of RGS2 alters the coupling of metabotropic glutamate receptor 1a to M-type K+ and N-type Ca2+ channels. Neuron 1999; 22:819-29. [PMID: 10230801 DOI: 10.1016/s0896-6273(00)80740-0] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Group I mGluRs heterologously expressed in sympathetic neurons inhibited calcium (I(Ca)) and M-type potassium (I(M)) currents. Treatment with pertussis toxin (PTX) revealed a voltage-dependent (VD), PTX-sensitive component of I(Ca) inhibition and a voltage-independent (VI), PTX-insensitive component. Coexpression of RGS2 occluded mGluR1a inhibition of I(M) and made I(Ca) inhibition VD in PTX-treated cells, presumably by blocking the effects of G alpha(q/11)-GTP. These data indicate that mGluR1a can couple to G(i/o) as well as G(q/11). In addition, VI I(Ca) inhibition proceeds through a G alpha(q/11)-GTP-mediated pathway, which can be occluded by expressing RGS2, leaving the VD, G betagamma-mediated inhibition active. These data may reveal a functional role for the upregulation of RGS2 expression in in vivo systems.
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Affiliation(s)
- P J Kammermeier
- Laboratory of Molecular Physiology, Guthrie Research Institute, Sayre, Pennsylvania 18840, USA
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2250
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Dutar P, Vu HM, Perkel DJ. Pharmacological characterization of an unusual mGluR-evoked neuronal hyperpolarization mediated by activation of GIRK channels. Neuropharmacology 1999; 38:467-75. [PMID: 10221750 DOI: 10.1016/s0028-3908(98)00206-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The metabotropic glutamate receptor (mGluR) agonist ACPD exerts an unusual inhibitory effect on a population of neurons of the song-control nucleus HVc of the zebra finch via activation of the GIRK channel. We report in the present study the pharmacology of this response. ACPD directly hyperpolarized the neurons by a mechanism independent of GABA(B) receptors. The group I mGluR agonist DHPG had no effect on membrane properties and the group I mGluR antagonist 4-CPG did not affect the ACPD-induced hyperpolarization. In contrast, the ACPD response was mimicked by the group II mGluR agonist LY314593 and the group II and III agonist L-CCG-I. The group II mGluR antagonist LY307452 fully antagonized the ACPD response and reduced the response induced by L-CCG-I. The group III mGluR agonist L-AP4 induced a small hyperpolarization, which was antagonized by the group III mGluR antagonist MAP-4. These data indicate that group II and group III mGluRs are present and functional in the postsynaptic membrane of these HVc neurons, and mediate the hyperpolarizing action of mGluR agonists. In contrast, group I mGluRs are absent from these neurons, nonfunctional, or coupled to different effector systems that do not influence membrane potential or input resistance.
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Affiliation(s)
- P Dutar
- Department of Neuroscience, University of Pennsylvania, Philadelphia 19104-6074, USA
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