201
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Koenig JI, Cho JY. Provocation of kainic acid receptor mRNA changes in the rat paraventricular nucleus by insulin-induced hypoglycaemia. J Neuroendocrinol 2005; 17:111-8. [PMID: 15796762 DOI: 10.1111/j.1365-2826.2005.01285.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hypoglycaemia induced by insulin injection is a powerful stimulus to the hypothalamic-pituitary-adrenal (HPA) axis and drives the secretion of corticotropin-releasing hormone and vasopressin from the neurones in the paraventricular nucleus (PVN), as well as the downstream hormones, adrenocorticotropic hormone and corticosterone. In some brain regions, hypoglycaemia also provokes increases in extracellular fluid concentrations of glutamate. Regulation of glutamatergic mechanisms could be involved in the control of the HPA axis during hypoglycaemic stress and one potential site of regulation might be at the receptors for glutamate, which are expressed in the PVN. Insulin (2.0 IU/kg, i.p.) or saline was administered to adult male Sprague-Dawley rats and the animals were sacrificed 30 min, 180 min and 24 h after injection. The amount of several kainic acid-preferring glutamate receptor mRNAs (i.e. KA2, GluR5 and GluR6) were assessed in the PVN by in situ hybridisation histochemistry. Injection of insulin induced a rapid fall in plasma glucose concentrations, which was mirrored by an increase in plasma corticosterone concentrations. KA2 and GluR5 mRNAs are highly expressed within the rat PVN, and responded to hypoglycaemia with robust increases in expression that endured beyond the period of hypoglycaemia itself. However, GluR6 mRNA is expressed in the areas adjacent to the PVN and hypoglycaemic stress failed to alter expression of this mRNA. These experiments suggest that kainic acid-preferring glutamate receptors are responsive to changes in plasma glucose concentrations and may participate in the activation of the PVN neurones during hypoglycaemic stress.
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Affiliation(s)
- J I Koenig
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, MD 21228, USA.
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202
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Swanson CJ, Bures M, Johnson MP, Linden AM, Monn JA, Schoepp DD. Metabotropic glutamate receptors as novel targets for anxiety and stress disorders. Nat Rev Drug Discov 2005; 4:131-44. [PMID: 15665858 DOI: 10.1038/nrd1630] [Citation(s) in RCA: 459] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Anxiety and stress disorders are the most commonly occurring of all mental illnesses, and current treatments are less than satisfactory. So, the discovery of novel approaches to treat anxiety disorders remains an important area of neuroscience research. Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system, and G-protein-coupled metabotropic glutamate (mGlu) receptors function to regulate excitability via pre- and postsynaptic mechanisms. Various mGlu receptor subtypes, including group I (mGlu(1) and mGlu(5)), group II (mGlu(2) and mGlu(3)), and group III (mGlu(4), mGlu(7) and mGlu(8)) receptors, specifically modulate excitability within crucial brain structures involved in anxiety states. In addition, agonists for group II (mGlu(2/3)) receptors and antagonists for group I (in particular mGlu(5)) receptors have shown activity in animal and/or human conditions of fear, anxiety or stress. These studies indicate that metabotropic glutamate receptors are interesting new targets to treat anxiety disorders in humans.
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Affiliation(s)
- Chad J Swanson
- Eli Lilly and Company, Neuroscience Division, Lilly Corporate Center DC 0510, Indianapolis, Indiana 46285, USA
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203
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Tyszkiewicz JP, Yan Z. beta-Amyloid peptides impair PKC-dependent functions of metabotropic glutamate receptors in prefrontal cortical neurons. J Neurophysiol 2005; 93:3102-11. [PMID: 15659527 DOI: 10.1152/jn.00939.2004] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The metabotropic glutamate receptors (mGluRs) have been implicated in cognition, memory, and some neurodegenerative disorders, including the Alzheimer's disease (AD). To understand how the dysfunction of mGluRs contributes to the pathophysiology of AD, we examined the beta-amyloid peptide (Abeta)-induced alterations in the physiological functions of mGluRs in prefrontal cortical pyramidal neurons. Two potential targets of mGluR signaling involved in cognition, the GABAergic system and the N-methyl-d-aspartate (NMDA) receptor, were examined. Activation of group I mGluRs with (S)-3,5-dihydroxyphenylglycine (DHPG) significantly increased the spontaneous inhibitory postsynaptic current (sIPSC) amplitude, and this effect was protein kinase C (PKC) sensitive. Treatment with Abeta abolished the DHPG-induced enhancement of sIPSC amplitude. On the other hand, activation of group II mGluRs with (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (APDC) significantly increased the NMDA receptor (NMDAR)-mediated currents via a PKC-dependent mechanism, and Abeta treatment also diminished the APDC-induced potentiation of NMDAR currents. In Abeta-treated slices, both DHPG and APDC failed to activate PKC. These results indicate that the mGluR regulation of GABA transmission and NMDAR currents is impaired by Abeta treatment probably due to the Abeta-mediated interference of mGluR activation of PKC. This study provides a framework within which the role of mGluRs in normal cognitive functions and AD can be better understood.
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Affiliation(s)
- Joanna P Tyszkiewicz
- Dept. of Physiology and Biophysics, State University of New York at Buffalo, 124 Sherman Hall, Buffalo, NY, 14214, USA
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204
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Liu X, Chi OZ, Weiss HR. Effects of metabotropic glutamate receptor stimulation on blood-brain barrier permeability during focal cerebral ischemia. Neurochem Res 2005; 29:1857-62. [PMID: 15532541 DOI: 10.1023/b:nere.0000042212.14137.6f] [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: 11/12/2022]
Abstract
This investigation was performed to evaluate whether ACPD [(1S, 3R)-1-aminocyclopentane-1, 3-dicarboxylic acid], a metabotropic glutamate receptor agonist, would enhance the degree of increase in blood-brain barrier (BBB) permeability caused by focal cerebral ischemia. In this study, male Wistar rats were placed in control (n = 7) and ACPD (n = 7) groups under isoflurane anesthesia. Twenty minutes after middle cerebral artery (MCA) occlusion, patches of 10(-5) M ACPD or normal saline were placed on the ischemic cortex (IC) for a period of 40 min. Patches were changed every 10 min. One hour after MCA occlusion, BBB permeability was determined by measuring the transfer coefficient (Ki) of [alpha-14C] aminoisobutyric acid. There were no statistical differences in systemic blood pressures and heart rates between these groups. Blood gases were within normal limits. In the control group, the Ki of ischemic cortex (IC) was 2.1 times that of the contralateral cortex (CC) (3.7+/-0.9 vs. 1.8+/-0.3 microl/g/min). In the ACPD group, the Ki of the IC was 3.3 times that of the CC (5.0+/-0.7 vs. 1.5+/-0.4 microl/g/min). The increase in Ki of the ACPD group in the ischemic cortex was significantly greater than that in the control group. There was no significant difference in the Ki of the CC between these groups. Our data suggest that activation metabotropic glutamate receptors in the cortex can further augment the increase in BBB permeability caused by focal ischemia.
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Affiliation(s)
- Xia Liu
- Department of Physiology & Biophysics and Anesthesiology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635, USA
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205
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Tsai VWW, Scott HL, Lewis RJ, Dodd PR. The role of group I metabotropic glutamate receptors in neuronal excitotoxicity in Alzheimer's disease. Neurotox Res 2005; 7:125-41. [PMID: 15639804 DOI: 10.1007/bf03033782] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Neurodegenerative diseases such as Huntington's disease, ischemia, and Alzheimer's disease (AD) are major causes of death. Recently, metabotropic glutamate receptors (mGluRs), a group of seven-transmembrane-domain proteins that couple to G-proteins, have become of interest for studies of pathogenesis. Group I mGluRs control the levels of second messengers such as inositol 1,4,5-triphosphate (IP3), Ca2+ ions and cAMP. They elicit the release of arachidonic acid via intracellular Ca2+ mobilization from intracellular stores such as mitochondria and endoplasmic reticulum. This facilitates the release of glutamate and could trigger the formation of neurofibrillary tangles, a pathological hallmark of AD. mGluRs regulate neuronal injury and survival, possibly through a series of downstream protein kinase and cysteine protease signaling pathways that affect mitochondrially mediated programmed cell death. They may also play a role in glutamate-induced neuronal death by facilitating Ca(II) mobilization. Hence, mGluRs have become a target for neuroprotective drug development. They represent a pharmacological path to a relatively subtle amelioration of neurotoxicity because they serve a modulatory rather than a direct role in excitatory glutamatergic transmission.
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Affiliation(s)
- Vicky W-W Tsai
- School of Molecular and Microbial Sciences and Institute for Molecular Bioscience, University of Queensland, Brisbane 4072 Australia
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206
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Tabata T, Araishi K, Hashimoto K, Hashimotodani Y, van der Putten H, Bettler B, Kano M. Ca2+ activity at GABAB receptors constitutively promotes metabotropic glutamate signaling in the absence of GABA. Proc Natl Acad Sci U S A 2004; 101:16952-7. [PMID: 15550547 PMCID: PMC529326 DOI: 10.1073/pnas.0405387101] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Type B gamma-aminobutyric acid receptor (GABABR) is a G protein-coupled receptor that regulates neurotransmitter release and neuronal excitability throughout the brain. In various neurons, GABABRs are concentrated at excitatory synapses. Although these receptors are assumed to respond to GABA spillover from neighboring inhibitory synapses, their function is not fully understood. Here we show a previously undescribed function of GABABR exerted independent of GABA. In cerebellar Purkinje cells, interaction of GABABR with extracellular Ca2+ (Ca(2+)o) leads to a constitutive increase in the glutamate sensitivity of metabotropic glutamate receptor 1 (mGluR1). mGluR1 sensitization is clearly mediated by GABABR because it is absent in GABABR1 subunit-knockout cells. However, the mGluR1 sensitization does not require G(i/o) proteins that mediate the GABABR's classical functions. Moreover, coimmunoprecipitation reveals complex formation between GABABR and mGluR1 in the cerebellum. These findings demonstrate that GABABR can act as Ca(2+)o-dependent cofactors to enhance neuronal metabotropic glutamate signaling.
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Affiliation(s)
- Toshihide Tabata
- Department of Cellular Neurophysiology, Graduate School of Medical Science, Kanazawa University, Kanazawa, Ishikawa 920-8640, Japan
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207
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Abstract
Metabotropic glutamate (mGlu) receptors, a family of G-protein-coupled receptors, are thought to signal through the phospholipase and inositol (1,4,5)-trisphosphate receptor system, or through the adenylyl cyclase and protein kinase C system. Rong et al. have recently identified a new phosphoinositide (PI) 3-kinase enhancer (PIKE-L) that links group I mGlu receptors (mGluRI) to PI 3-kinase through Homer proteins, adaptors that bind mGluRI. mGluRI agonists enhanced mGluRI-Homer-PIKE-L complex formation, leading to activation of PI 3-kinase and inhibition of staurosporine-induced neuronal apoptosis. These results reveal a novel anti-apoptotic signaling mechanism that involves formation of an mGluRI signaling complex.
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Affiliation(s)
- N Guhan
- Section on Neural Development and Plasticity, NICHD/NIH, Bethesda, MD 20892-4480, USA
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208
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L-Glutamate in formation of long-term memory in the honeybee Apis mellifera. J EVOL BIOCHEM PHYS+ 2004. [DOI: 10.1007/s10893-005-0023-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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209
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Kammermeier PJ, Yun J. Activation of metabotropic glutamate receptor 1 dimers requires glutamate binding in both subunits. J Pharmacol Exp Ther 2004; 312:502-8. [PMID: 15466247 DOI: 10.1124/jpet.104.073155] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Group I metabotropic glutamate receptors (mGluRs) form stable, disulfide-linked homodimers. Lack of a verifiably monomeric mGluR1 mutant has led to difficulty in assessing the role of dimerization in the molecular mechanism of mGluR1 activation. The related GABA(B) receptor exhibits striking intradimer cross talk (ligand binding at one subunit effectively produces G protein activation at the other), but it is unclear whether group I mGluRs exhibit analogous cross talk. Signaling of heterologously expressed mGluR1 was examined in isolated rat sympathetic neurons by measuring glutamate-mediated inhibition of native calcium currents. To examine mGluR1 activity when only one dimer subunit has access to glutamate ligand, wildtype mGluR1 was coexpressed with mGluR1 Y74A, a mutant with impaired glutamate binding, and the activity of the heterodimer (mutant/wild type) was examined. The mGluR1 Y74A mutant alone had a dose-response curve that was shifted by about 2 orders of magnitude. The half-maximal dose of glutamate shifted from 1.3 (wild-type mGluR1) to about 450 (mGluR1 Y74A) microM. However, the maximal effect was similar. Wild-type mGluR1 was expressed with excess Y74A mGluR1 to generate a receptor population consisting largely of mutant homodimers and mutant/wild-type heterodimers but without detectable wild-type homodimers. Under these conditions, no glutamate-mediated calcium current inhibition was observed below approximately 300 microM glutamate, although wild-type mGluR1 protein was detectable with immunofluorescence. These data suggest that mutant/wild-type heterodimeric receptors are inactive at ligand concentrations favoring glutamate association with receptor dimers at only one subunit.
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Affiliation(s)
- Paul J Kammermeier
- Department of Physiology and Pharmacology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, P.O. Box 95, Rootstown, OH 44272, USA.
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210
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Tabata T, Kano M. Calcium dependence of native metabotropic glutamate receptor signaling in central neurons. Mol Neurobiol 2004; 29:261-70. [PMID: 15181238 DOI: 10.1385/mn:29:3:261] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2003] [Accepted: 11/17/2003] [Indexed: 11/11/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) are G protein-coupled receptors that are distributed throughout the brain and play important roles in regulation of synaptic efficacy. Some studies report that mGluRs heterologously expressed in nonneuronal cells are sensitive not only to glutamate but also to extracellular Ca2+ (Ca2+o). We studied the Ca2+o-sensitivity of native mGluRs in mammalian central neurons. In cerebellar Purkinje cells that naturally express type-1 mGluR (mGluR1), physiological levels of Ca2+o (around 2 mM) activate mGluR1-mediated intracellular Ca2+ mobilization. The activation of the native mGluR1 response to Ca2+o appears to be slower than that to glutamate. Ca2+o (2 mM) also augments glutamate analog-evoked, native mGluR1-mediated inward cation current and intracellular Ca2+o mobilization. Detailed analysis of this effect suggests that Ca2+o modulates the glutamate responsiveness of native and heterologously expressed mGluR1s in different manners. These findings suggest that Ca2+o may enhance the basal level and glutamate responsiveness of neuronal mGluR signaling in vivo.
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Affiliation(s)
- Toshihide Tabata
- Department of Cellular Neurophysiology, Graduate School of Medical Science, Kanazawa University, Kanazawa, Ishikawa 920-8640, Japan.
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211
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Vlkolinský R, Siggins GR, Campbell IL, Krucker T. Acute exposure to CXC chemokine ligand 10, but not its chronic astroglial production, alters synaptic plasticity in mouse hippocampal slices. J Neuroimmunol 2004; 150:37-47. [PMID: 15081247 DOI: 10.1016/j.jneuroim.2004.01.011] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2003] [Revised: 01/12/2004] [Accepted: 01/12/2004] [Indexed: 11/18/2022]
Abstract
Brain levels of CXC chemokine ligand 10 (CXCL10) are elevated in a number of neuropathological conditions. To determine its impact on neuronal function, we measured synaptic transmission and plasticity in hippocampal slices prepared from transgenic (TG) mice with chronic astroglial production of CXCL10. We also tested the acute effect of recombinant CXCL10 applied to slices from normal C57Bl/6J mice, CXCL10 TG mice and CXCR3 knock out (KO) mice. Chronic production of CXCL10 did not alter synaptic plasticity. By contrast, exogenous CXCL10 (10 ng/ml) significantly inhibited long-term potentiation (LTP) in slices from normal C57Bl/6J mice and CXCL10 TG. The effect was probably receptor-mediated because CXCL10-induced inhibition of LTP was not observed in CXCR3 KO mice. Our findings suggest that acute exposure to CXCL10 alters synaptic plasticity via CXCR3 in mouse hippocampus.
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MESH Headings
- Animals
- Astrocytes/immunology
- Astrocytes/metabolism
- Astrocytes/physiology
- Chemokine CXCL10
- Chemokines, CXC/biosynthesis
- Chemokines, CXC/genetics
- Chemokines, CXC/pharmacology
- Chemokines, CXC/physiology
- Excitatory Postsynaptic Potentials/genetics
- Excitatory Postsynaptic Potentials/immunology
- In Vitro Techniques
- Long-Term Potentiation/genetics
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Neural Inhibition/genetics
- Neural Inhibition/immunology
- Neuronal Plasticity/genetics
- Neuronal Plasticity/immunology
- Receptors, CXCR3
- Receptors, Chemokine/deficiency
- Receptors, Chemokine/genetics
- Receptors, Chemokine/physiology
- Recombinant Proteins/pharmacology
- Synapses/genetics
- Synapses/immunology
- Time Factors
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Affiliation(s)
- Roman Vlkolinský
- Department of Neuropharmacology, CVN-12, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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212
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Saransaari P, Oja SS. Metabotropic glutamate receptors modulate ischemia-induced GABA release in mouse hippocampal slices. Neurochem Res 2004; 29:1511-8. [PMID: 15260128 DOI: 10.1023/b:nere.0000029563.94579.f6] [Citation(s) in RCA: 7] [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
The involvement of glutamate receptors in GABA release in ischemia was investigated in hippocampal slices from adult (3-month-old) and developing (7-day-old) mice. For in vitro ischemia, the slices were superfused in glucose-free media under nitrogen. Ionotropic glutamate receptor agonists failed to affect the ischemia-induced basal GABA release at either age. The K(+)-stimulated release in the immature hippocampus was potentiated by N-methyl-D-aspartate receptors, whereas in adults this release was reduced by both kainate and 2-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate receptor activation. The group I metabotropic receptor agonist (1+/-)-1-aminocyclopentane-trans-1,3-dicarboxylate enhanced the basal ischemic GABA release in a receptor-mediated manner in adults, this being concordant with the positive modulation of GABAergic neurotransmission by group I metabotropic glutamate receptors. (1 +/-)-1-Aminocyclopentane-trans-1,3-dicarboxylate and (S)-3,5-dihydroxyphenylglycine also enhanced the K(+)-stimulated release in the developing hippocampus in a receptor-mediated manner. Because group I receptors generally increase neuronal excitability, the enhanced GABA release may attenuate hyperexcitation or strengthen inhibition, being thus neuroprotective, particularly under ischemic conditions. Group III metabotropic glutamate receptors were not at all involved in ischemic GABA release in the immature mice, but in adults their activation by O-phospho-L-serine potentiated the basal release and reduced the K(+)-stimulated release. These opposite effects were abolished by the antagonist (RS)-2-cyclopropyl-4-phosphonophenylglycine. Metabotropic glutamate receptors, namely group I and III receptors, are able to modify the release of GABA from hippocampal slices under ischemic conditions, both positive and negative effects being discernible, depending on the age and type of receptor activated.
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Affiliation(s)
- Pirjo Saransaari
- Tampere Brain Research Center, Medical School, FIN-33014 University of Tampere, Finland.
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213
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Ai J, Baker A. Presynaptic Excitability as a Potential Target for the Treatment of the Traumatic Cerebellum. Pharmacology 2004; 71:192-8. [PMID: 15240995 DOI: 10.1159/000078085] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2003] [Accepted: 12/17/2003] [Indexed: 11/19/2022]
Abstract
Using an extracellular recording method, we have previously shown a hyperexcitability of the presynaptic response in fluid percussion injury (FPI) in rats. In this study, we demonstrated that treatment with cis-ACBD, a glutamate reuptake inhibitor, depressed the presynaptic potential (PSP) in naive/sham controls, while it potentiated the PSP in FPI rats. On the contrary, (RS)-APICA, a selective group II metabotropic glutamate receptor antagonist, potentiated PSP in controls, but depressed PSP in FPI rats. These results indicate that an alteration of the normal function of metabotropic glutamate receptors and glutamate reuptake system or an altered reactivity of presynaptic fibers was induced by FPI. This alteration may contribute to the reported loss of Purkinje cells after FPI. PSP may be used as a potential tool for evaluating treatments of FPI or as a potential target for the prevention of Purkinje cell death.
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Affiliation(s)
- Jinglu Ai
- Traumatic Brain Injury Laboratory, Cara Phelan Centre for Trauma Research, St. Michael's Hospital, University of Toronto, Toronto, Ont., Canada.
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214
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Takaki H, Kikuta R, Shibata H, Ninomiya H, Tashiro N, Fukumaki Y. Positive associations of polymorphisms in the metabotropic glutamate receptor type 8 gene (GRM8) with schizophrenia. Am J Med Genet B Neuropsychiatr Genet 2004; 128B:6-14. [PMID: 15211621 DOI: 10.1002/ajmg.b.20108] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The glutamatergic dysfunction has been implicated in pathophysiology of schizophrenia. The Group III metabotropic glutamate receptor 4 (mGluR4), 6, 7, and 8 are thought to modulate glutamatergic transmission in the brain by inhibiting glutamate release at the synapse. We tested association of schizophrenia with GRM8 using 22 single nucleofide polymorphisms (SNPs) with the average intervals of 40.3 kb in the GRM8 region in 100 case-control pairs for the SNPs. Although we observed significant associations of schizophrenia with two SNPs, SNP18 (rs2237748, allele: P = 0.0279; genotype: P = 0.0124) and SNP19 (rs2299472, allele: P = 0.0302; genotype: P = 0.0127), none of two SNPs showed significant association with disease after Bonferroni correction. Both SNP18 and SNP19 were included in a large region (>330 kb) in which SNPs are in linkage disequilibrium (LD) at the 3' region of GRM8. We also tested haplotype association of schizophrenia with constructed haplotypes of the SNPs in LD. Significant associations were detected for the combinations of SNP5-SNP6 (chi(2) = 18.12, df = 3, P = 0.0004, P corr = 0.0924 with Bonferroni correction), SNP4-SNP5-SNP6 (chi(2) = 27.50, df = 7, P = 0.0075, P corr = 0.015 with Bonferroni correction), and SNP5-SNP6-SNP7 (chi(2) = 23.92, df = 7, P = 0.0011, P corr = 0.0022 with Bonferroni correction). Thus, we conclude that at least one susceptibility locus for schizophrenia is located within the GRM8 region in Japanese.
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Affiliation(s)
- Hiromi Takaki
- Division of Disease Genes, Research Center For Genetic Information, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
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215
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Acuna-Goycolea C, Li Y, Van Den Pol AN. Group III metabotropic glutamate receptors maintain tonic inhibition of excitatory synaptic input to hypocretin/orexin neurons. J Neurosci 2004; 24:3013-22. [PMID: 15044540 PMCID: PMC6729849 DOI: 10.1523/jneurosci.5416-03.2004] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Hypocretin/orexin neurons play an important role in hypothalamic arousal. Synaptic glutamate input to hypocretin neurons regulates cell firing. We studied the actions of group III metabotropic glutamate receptors (mGluRs) in modulating the activity of hypocretin neurons using whole-cell voltage- and current-clamp recording in mouse whole hypothalamic slices or minislices consisting only of the lateral hypothalamus. Selective green fluorescent protein expression was used to detect live hypocretin neurons. The mGluR agonist l-(+)-2-amino-4-phosphonobutyric acid (l-AP-4) inhibited synaptic input to hypocretin neurons in a dose-dependent manner; both spontaneous glutamate and GABA-mediated synaptic currents were reduced in frequency. l-AP-4 also reduced the amplitude of postsynaptic potentials evoked by a stimulating electrode placed medial or lateral to the recorded cell. No postsynaptic effect of l-AP-4 was found relative to membrane potential, input resistance, or AMPA-evoked currents. l-AP-4 appeared to act by a presynaptic mechanism and reduced the frequency of both glutamate- and GABA-mediated miniature events recorded in the presence of tetrodotoxin, with no change in amplitude. (RS)-phosphonopentanoic acid (CPPG), a group III mGluR antagonist, suppressed the actions of l-AP-4. Of substantial interest, CPPG by itself increased synaptic activity recorded in hypocretin neurons, suggesting an ongoing inhibitory tone attributable to activation of group III mGluRs. Glutamatergic interneurons have been suggested to play a role in a positive feedback recruitment of hypocretin on hypocretin neurons. l-AP-4 blocked hypocretin-mediated increases in EPSCs and attenuated the hypocretin-mediated increase in spike frequency. Together, these data suggest that tonically active inhibitory mGluRs are expressed on local hypocretin-sensitive glutamate neurons within the lateral hypothalamus that modulate the output of the hypocretin arousal system.
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Affiliation(s)
- Claudio Acuna-Goycolea
- Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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216
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Pula G, Mundell SJ, Roberts PJ, Kelly E. Agonist-independent internalization of metabotropic glutamate receptor 1a is arrestin- and clathrin-dependent and is suppressed by receptor inverse agonists. J Neurochem 2004; 89:1009-20. [PMID: 15140199 DOI: 10.1111/j.1471-4159.2004.02387.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Three group I mGluR antagonists CPCCOEt, LY367385 and BAY36-7620, were analyzed for their effect on cell surface expression of metabotropic glutamate receptor 1a and 1b. All three antagonists inhibited glutamate-induced internalization of mGluR1a and mGluR1b. However, when added alone, either LY367385 or BAY36-7620 increased the cell surface expression of mGluR1a but not mGluR1b. Both LY367385 and BAY36-7620 displayed inverse agonist activity as judged by their ability to inhibit basal inositol phosphate accumulation in cells expressing the constitutively active mGluR1a. Interestingly, mGluR1a but not mGluR1b was constitutively internalized in HEK293 cells and both LY367385 and BAY36-7620 inhibited the constitutive internalization of this splice variant. Furthermore, coexpression of dominant negative mutant constructs of arrestin-2 [arrestin-2-(319-418)] or Eps15 [Eps15(E Delta 95-295)] increased cell surface expression of mGluR1a and blocked constitutive receptor internalization. In the presence of these dominant negative mutants, incubation of cells with LY367385 and BAY36-7620 produced no further increase in cell surface expression of mGluR1a. Taken together, these results suggest that the constitutive activity of mGluR1a triggers the internalization of the receptor through an arrestin- and clathrin-dependent pathway, and that inverse agonists increase the cell surface expression of mGluR1a by promoting an inactive form of mGluR1a, which does not undergo constitutive internalization.
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Affiliation(s)
- Giordano Pula
- Department of Pharmacology, School of Medical Sciences, University of Bristol, Bristol, UK
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Benz B, Grima G, Do KQ. Glutamate-induced homocysteic acid release from astrocytes: possible implication in glia-neuron signaling. Neuroscience 2004; 124:377-86. [PMID: 14980387 DOI: 10.1016/j.neuroscience.2003.08.067] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2002] [Revised: 08/13/2003] [Accepted: 08/22/2003] [Indexed: 11/30/2022]
Abstract
Glial cells synthesise neuroactive substances and release them upon neurotransmitter receptor activation. Homocysteic acid (HCA), an endogenous agonist for glutamatergic N-methyl-D-aspartate (NMDA) receptors, is predominantly localised in glial cells. We have previously demonstrated the release of HCA from mouse astrocytes in culture following activation of beta-adrenergic receptors. Moreover, a release of HCA has also been observed in vivo upon physiological stimulation of sensory afferents in the thalamus. Here we report the glutamate-induced release of HCA from astrocytes. The effect of glutamate was mediated by the activation of ionotropic (NMDA and non-NMDA) as well as by metabotropic receptors. In addition, the release of HCA was Ca(2+)- and Na(+)-dependent, and its mechanism involved the activation of the Na+/Ca(2+)-exchanger. Furthermore, we provide evidence for the presence of functional NMDA receptors on astrocytes, which are coupled to an intracellular Ca2+ increase via stimulation of the Na+/Ca(2+)-exchanger. Our data thus favour a participation of glial cells in excitatory neurotransmission and corroborate the role of HCA as a "gliotransmitter."
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Affiliation(s)
- B Benz
- Centre for Research in Psychiatric Neuroscience, Department of Psychiatry, University of Lausanne, Route de Cery, CH-1008 Prilly-Lausanne, Switzerland
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218
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Iacovelli L, Capobianco L, Iula M, Di Giorgi Gerevini V, Picascia A, Blahos J, Melchiorri D, Nicoletti F, De Blasi A. Regulation of mGlu4 metabotropic glutamate receptor signaling by type-2 G-protein coupled receptor kinase (GRK2). Mol Pharmacol 2004; 65:1103-10. [PMID: 15102938 DOI: 10.1124/mol.65.5.1103] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined the role of G-protein coupled receptor kinase-2 (GRK2) in the homologous desensitization of mGlu4 metabotropic glutamate receptors transiently expressed in human embryonic kidney (HEK) 293 cells. Receptor activation with the agonist l-2-amino-4-phosphonobutanoate (l-AP4) stimulated at least two distinct signaling pathways: inhibition of cAMP formation and activation of the mitogen-activated protein kinase (MAPK) pathway [assessed by Western blot analysis of phosphorylated extracellular signal-regulated kinase (ERK) 1 and 2]. Activation of both pathways was attenuated by pertussis toxin. Overexpression of GRK2 (but not GRK4) largely attenuated the stimulation of the MAPK pathway by l-AP4, whereas it slightly potentiated the inhibition of FSK-stimulated cAMP formation. Transfection with a kinase-dead mutant of GRK2 (GRK2-K220R) or with the C-terminal fragment of GRK2 also reduced the mGlu4-mediated stimulation of MAPK, suggesting that GRK2 binds to the Gbetagamma subunits to inhibit signal propagation toward the MAPK pathway. This was confirmed by the evidence that GRK2 coimmunoprecipitated with Gbetagamma subunits in an agonist-dependent manner. Finally, neither GRK2 nor its kinase-dead mutant had any effect on agonist-induced mGlu4 receptor internalization in HEK293 cells transiently transfected with GFP-tagged receptors. Agonist-dependent internalization was instead abolished by a negative-dominant mutant of dynamin, which also reduced the stimulation of MAPK pathway by l-AP4. We speculate that GRK2 acts as a "switch molecule" by inhibiting the mGlu4 receptor-mediated stimulation of MAPK and therefore directing the signal propagation toward the inhibition of adenylyl cyclase.
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Affiliation(s)
- L Iacovelli
- Dept. of Human Physiology and Pharmacology, University of Rome La Sapienza, Italy.
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219
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Chaki S, Yoshikawa R, Hirota S, Shimazaki T, Maeda M, Kawashima N, Yoshimizu T, Yasuhara A, Sakagami K, Okuyama S, Nakanishi S, Nakazato A. MGS0039: a potent and selective group II metabotropic glutamate receptor antagonist with antidepressant-like activity. Neuropharmacology 2004; 46:457-67. [PMID: 14975669 DOI: 10.1016/j.neuropharm.2003.10.009] [Citation(s) in RCA: 212] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2003] [Revised: 10/06/2003] [Accepted: 10/14/2003] [Indexed: 11/30/2022]
Abstract
The present study describes the pharmacological profile of (1R,2R,3R,5R,6R)-2-Amino-3-(3,4-dichlorobenzyloxy)-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (MGS0039), a novel group II mGluR antagonist. MGS0039 showed high affinity for both mGluR2 (Ki = 2.2 nM) and mGluR3 (Ki = 4.5 nM), which are comparable to LY341495, another group II mGluR antagonist. MGS0039 attenuated both glutamate-induced inhibition of forskolin-evoked cyclic AMP formation in CHO cells expressing mGluR2 (IC50 = 20 nM) or mGluR3 (IC50 = 24 nM) and glutamate-increased [35S]GTPgammaS binding to mGluR2 (pA2 = 8.2), which means that MGS0039 acts as an antagonist. MGS0039 shifted the dose-response curve of glutamate-increased [35S]GTPgammaS binding rightward without altering the maximal response, and thereby indicating competitive antagonism. MGS0039 showed no significant effects on other mGluRs as well as the other receptors and transporters we studied. MGS0039 (0.3-3 mg/kg, i.p.) as well as LY341495 (0.1-3 mg/kg, i.p.) had dose-dependent antidepressant-like effects in the rat forced swim test and in the mouse tail suspension test. In contrast, MGS0039 (0.3-3 mg/kg, i.p.) had no apparent effect in the rat social interaction test and in the rat elevated plus-maze. These results indicate that MGS0039 is a potent and selective antagonist of group II mGluR, and that group II mGluR antagonists, like MGS0039, have an antidepressant-like potential in experimental animal models.
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Affiliation(s)
- Shigeyuki Chaki
- Medicinal Research Laboratories, Taisho Pharmaceutical Co., Ltd., Saitama 331-9530, Japan.
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220
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Buratta S, Mambrini R, Miniaci MC, Tempia F, Mozzi R. Group I metabotropic glutamate receptors mediate the inhibition of phosphatidylserine synthesis in rat cerebellar slices: a possible role in physiology and pathology. J Neurochem 2004; 89:730-8. [PMID: 15086529 DOI: 10.1046/j.1471-4159.2004.02403.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In cerebellar slices, the lowering of oxygen availability, obtained by bubbling N(2) in the medium, reduced the incorporation of radioactive serine into phosphatidylserine (PtdSer). CPCCOEt, an antagonist of metabotropic glutamate receptors type 1 (mGluR1) counteracted the effect, whereas antagonists of NMDA or AMPA receptors were ineffective. In oxygenated slices, agonists of Group I mGluRs, which include mGluR1, inhibited PtdSer synthesis. This effect was also counteracted by CPCCOEt. These findings indicate that glutamate inhibits PtdSer synthesis by acting on mGluR1. This could be important in relation to the known release of glutamate in hypoxia-ischaemia conditions. In cerebellar Purkinje cells, mGluR1 are involved in the generation of mGluR-EPSP evoked by parallel fibre stimulation. The administration of l-serine to cerebellar slices reduced in a dose-dependent manner the mGluR-EPSP evoked by parallel fibre stimulation. The effect was mostly due to the increased synthesis of PtdSer. Thus inhibition of PtdSer synthesis, mediated by mGluR1, may participate in the generation of mGluR-EPSP.
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Affiliation(s)
- Sandra Buratta
- Department of Internal Medicine, Section of Biochemistry, University of Perugia, Perugia, Italy
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221
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Wehbe J, Rolland V, Fruchier A, Roumestant ML, Martinez J. Enantioselective synthesis of new 4-substituted glutamic acid derivatives. ACTA ACUST UNITED AC 2004. [DOI: 10.1016/j.tetasy.2004.01.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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222
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Cox CL. Synaptic Activation of Metabotropic Glutamate Receptors Regulates Dendritic Outputs of Thalamic Interneurons. Neuron 2004; 41:611-23. [PMID: 14980209 DOI: 10.1016/s0896-6273(04)00013-3] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2003] [Revised: 11/26/2003] [Accepted: 01/06/2004] [Indexed: 10/26/2022]
Abstract
Information gating through the thalamus is dependent on the output of thalamic relay neurons. These relay neurons receive convergent innervation from a number of sources, including GABA-containing interneurons that provide feed-forward inhibition. These interneurons are unique in that they have two distinct outputs: axonal and dendritic. In addition to conventional axonal outputs, these interneurons have presynaptic dendrites that may provide localized inhibitory influences. Our study indicates that synaptic activation of metabotropic glutamate receptors (mGluRs) increases inhibitory activity in relay neurons by increasing output of presynaptic dendrites of interneurons. Optic tract stimulation increases inhibitory activity in thalamic relay neurons in a frequency- and intensity-dependent manner and is attenuated by mGluR antagonists. Our data suggest that synaptic activation of mGluRs selectively alters dendritic output but not axonal output of thalamic interneurons. This mechanism could serve an important role in focal, feed-forward information processing in addition to dynamic information processing in thalamocortical circuits.
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223
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Lopatina NG, Ryzhova IV, Zachepilo TG, Smirnov VB, Chesnokova EG. L-Glutamate in formation of long-term memory in the honeybee Apis mellifera. J EVOL BIOCHEM PHYS+ 2004. [DOI: 10.1007/s10893-004-0007-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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224
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Riddle R, Pollock JD. Making connections: the development of mesencephalic dopaminergic neurons. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2003; 147:3-21. [PMID: 14741747 DOI: 10.1016/j.devbrainres.2003.09.010] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The disorders of two adjacent sets of mesencephalic dopaminergic (MDNs) are associated with two significant health problems: Parkinson's disease and drug addiction. Because of this, a great deal of research has focused on understanding the growth, development and maintenance of MDNs. Many transcription factors and signaling pathways are known to be required for normal MDNs formation, but a unified model of MDN development is still unclear. The long-term goal is to design therapeutic strategies to: (i) nurture and/or heal endogenous MDNs, (ii) replace the affected tissue with exogenous MDNs from in vitro cultivated stem cells and (iii) restore normal connectivity. Recent developmental biology studies show great promise in understanding how MDNs develop both in vivo and in vitro. This information has great therapeutic value and may provide insight into how environmental and genetic factors increase vulnerability to addiction.
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Affiliation(s)
- Robert Riddle
- Genetics and Molecular Neurobiology Research Branch, Division of Neuroscience and Behavioral Research, National Institute on Drug Abuse, 6001 Executive Blvd., Bethesda, MD 20892-9555, USA.
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225
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Smith SK, Hoogendoorn B, Guy CA, Coleman SL, O'Donovan MC, Buckland PR. Lack of functional promoter polymorphisms in genes involved in glutamate neurotransmission. Psychiatr Genet 2003; 13:193-9. [PMID: 14639045 DOI: 10.1097/00041444-200312000-00001] [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: 11/26/2022]
Abstract
OBJECTIVES The regulation of genes involved in glutamatergic function is thought to be a critical for many central nervous system processes including memory, learning, synaptic maintenance, and many pathological states. As part of a larger survey into the key regulatory elements in genes of neuro-psychiatric interest, we sought to identify the promoter regions of genes in this broad family, and to identify sequence variants that alter gene expression. METHODS Mutation analysis was carried out on the promoters of 20 genes encoding 13 glutamate receptor subunits, four transporters and three metabolizing enzymes using denaturing high performance liquid chromatography. Thirty-nine different promoter haplotypes were cloned into a luciferase reporter gene vector and tested for differences in their ability to drive transcription in both HEK293t and TE671 cell lines. RESULTS We have identified a total of 48 sequence variants in six glutamate receptor subunits, four glutamate transporters and two enzymes. Interestingly, seven promoter sequences gave three or more haplotypes from a single individual, indicating gene duplication. No differences in expression greater than 1.35-fold were found between haplotypes originating from the same or paralogous genes. CONCLUSION The lack of common functional polymorphisms in any of these promoters indicates that expression of glutamate receptors and transporters is unusually tightly controlled, and suggests the possibility that non-coding polymorphisms in these genes are rare and may be unlikely to contribute in a major way to neuro-psychiatric phenotypes. This study represents the world's largest survey of the any group of promoters yet performed for any gene system.
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Affiliation(s)
- S K Smith
- Department of Psychological Medicine, University of Wales College of Medicine, Cardiff, UK
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226
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Arce C, Del Campo AB, Figueroa S, López E, Aránguez I, Oset-Gasque MJ, González MP. Expression and functional properties of group I metabotropic glutamate receptors in bovine chromaffin cells. J Neurosci Res 2003; 75:182-193. [PMID: 14705139 DOI: 10.1002/jnr.10824] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We demonstrate the presence and functional properties of Group I metabotropic glutamate receptors (mGluRs) expressed in chromaffin cells. Immunocytochemical techniques revealed that two mGluR subtypes (mGluR1alpha and mGluR5) are expressed in chromaffin cells, located in both the cytoplasmic membrane and the cytosol surrounding the nucleus. These mGluRs are functionally active on catecholamine (CA) secretion in chromaffin cells because both (1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD) and the specific agonist of Group I mGluRs, (S)-3,5-dihydroxyphenylglycine (DHPG), were able to stimulate the release of CAs (adrenaline and noradrenaline) in a dose-response manner. These effects were specifically reversed by L-(+)-2-amino-3-phosphonopropionic acid (L-AP3), a selective antagonist of the Group I metabotropic glutamate receptors. t-ACPD induced an increase in CA secretion in both the presence and absence of extracellular calcium, the former effect being accompanied by cell membrane depolarization. Noradrenaline (NA) release was higher in the presence of extracellular calcium than in its absence, whereas adrenaline release was of the same order under both conditions. These results indicate that different subtypes of Group I mGluRs are present in noradrenergic and adrenergic cells. Fluorescence imaging techniques in single cells showed different t-ACPD-induced increases in intracellular calcium in different chromaffin cells: in chromaffin cells, 67% expressed functional metabotropic glutamate receptors and with nicotinic receptors, whereas the remaining 33% expressed only nicotinic receptors. In the absence of external calcium, only about 25% of cells responded to t-ACPD-increased intracellular calcium by increasing inositol 1,4,5-trisphosphate (IP(3)) concentration and subsequent calcium mobilization from intracellular stores, whereas the remaining 75% increased intracellular calcium by promoting Ca(2+) influx from the extracellular medium through L- and N- but not P/Q voltage-dependent calcium channels.
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Affiliation(s)
- C Arce
- Instituto de Bioquímica (Centro Mixto CSIC-UCM), Facultad de Farmacia, Madrid, Spain
| | - A B Del Campo
- Instituto de Bioquímica (Centro Mixto CSIC-UCM), Facultad de Farmacia, Madrid, Spain
| | - S Figueroa
- Instituto de Bioquímica (Centro Mixto CSIC-UCM), Facultad de Farmacia, Madrid, Spain
| | - E López
- Instituto de Bioquímica (Centro Mixto CSIC-UCM), Facultad de Farmacia, Madrid, Spain
| | - I Aránguez
- Instituto de Bioquímica (Centro Mixto CSIC-UCM), Facultad de Farmacia, Madrid, Spain
| | - M J Oset-Gasque
- Instituto de Bioquímica (Centro Mixto CSIC-UCM), Facultad de Farmacia, Madrid, Spain
| | - M P González
- Instituto de Bioquímica (Centro Mixto CSIC-UCM), Facultad de Farmacia, Madrid, Spain
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Sinhorin VDG, Carpes MJS, Roehrs C, Zimmer MF, Sauzem PD, Rubin MA, Correia CRD, Mello CF. D,L-cis-2,3-Pyrrolidine dicarboxylate alters [3H]-L-glutamate binding and induces convulsions in mice. Pharmacol Biochem Behav 2003; 76:295-9. [PMID: 14592681 DOI: 10.1016/j.pbb.2003.08.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This study investigated whether D,L-cis-2,3-Pyrrolidine dicarboxylate (D,L-cis-2,3-PDC), a new glutamate analogue, alters glutamate binding to cerebral plasma membranes and whether N-methyl-D-aspartate (NMDA) receptors are involved in the convulsant effect of this compound. D,L-cis-2,3-PDC reduced sodium-independent [3H]-L-glutamate binding to lysed membrane preparations from adult rat cortex and had no effect on sodium-dependent glutamate binding. Intracerebroventricular administration of D,L-cis-2,3-PDC (7.5-25 nmol/5 microl) induced generalized tonic-clonic convulsions in mice in a dose-dependent manner. The coadministration of MK-801 (7 nmol/2.5 microl), with D,L-cis-2,3-PDC (16.5 nmol/2.5 microl), fully protected the animals against D,L-cis-2,3-PDC-induced convulsions, while the coadministration of DNQX (10 nmol/2.5 microl) increased the latency to convulsions but did not alter the percentage of animals that had convulsions. These results suggest that D,L-cis-2,3-PDC-induced effects are mediated predominantly by NMDA receptors.
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Affiliation(s)
- Valéria Dornelles Gindri Sinhorin
- Centro de Ciências Naturais e Exatas, Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil
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228
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Role of thalamic phospholipase C[beta]4 mediated by metabotropic glutamate receptor type 1 in inflammatory pain. J Neurosci 2003. [PMID: 12954872 DOI: 10.1523/jneurosci.23-22-08098.2003] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Phospholipase C (PLC) beta4, one of the four isoforms of PLCbetas, is the sole isoform expressed in the mouse ventral posterolateral thalamic nucleus (VPL), a key station in pain processing. The mouse thalamus also has been shown to express a high level of metabotropic glutamate receptor type 1 (mGluR1), which stimulates PLCbetas through activation of Galphaq/11 protein. It is therefore expected that the thalamic mGluR1-PLCbeta4 cascade may play a functional role in nociceptive transmission. To test this hypothesis, we first studied behavioral responses to various nociceptive stimuli in PLCbeta4 knock-out mice. We performed the formalin test and found no difference in the pain behavior in the first phase of the formalin test, which is attributed to acute nociception, between PLCbeta4 knock-out and wild-type mice. Consistent with this result, acute pain responses in the hot plate and tail flick tests were also unaffected in the PLCbeta4 knock-out mice. However, the nociceptive behavior in the second phase of the formalin test, resulting from the tissue inflammation, was attenuated in PLCbeta4 knock-out mice. In the dorsal horn of the spinal cord where PLCbeta1 and PLCbeta4 mRNAs are expressed, no difference was found between the wild-type and knock-out mice in the number of Fos-like immunoreactive neurons, which represent neuronal activity in the second phase in the formalin test. Thus, it is unlikely that spinal PLCbeta4 is involved in the formalin-induced inflammatory pain. Next, we found that pretreatment with PLC inhibitors, mGluR1 antagonists, or both, by either intracerebroventricular or intrathalamic injection, attenuated the formalin-induced pain behavior in the second phase in wild-type mice. Furthermore, activation of mGluR1 at the VPL enhanced pain behavior in the second phase in the wild-type mice. In contrast, PLCbeta4 knock-out mice did not show such enhancement, indicating that mGluR1 is connected to PLCbeta4 in the VPL. Finally, in parallel with the behavioral results, we showed in an electrophysiological study that the time course of firing discharges in VPL corresponds well to that of pain behavior in the formalin test in both wild-type and PLCbeta4 knock-out mice. These findings indicate that the thalamic mGluR1-PLCbeta4 cascade is indispensable for the formalin-induced inflammatory pain by regulating the response of VPL neurons.
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229
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O'Neill MF, Heron-Maxwell C, Conway MW, Monn JA, Ornstein P. Group II metabotropic glutamate receptor antagonists LY341495 and LY366457 increase locomotor activity in mice. Neuropharmacology 2003; 45:565-74. [PMID: 12941370 DOI: 10.1016/s0028-3908(03)00232-6] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The group II metabotropic glutamate receptor (mGluR) antagonists LY341495 and LY366457 were profiled for their effects on locomotor activity in mice. Both compounds significantly increased locomotor activity. Observational studies showed that rearing was also selectively increased. LY366457-induced hyperactivity was significantly attenuated by the selective D1 dopamine receptor antagonist SCH23390 and also by the D2 dopamine receptor antagonist haloperidol but only at doses that significantly suppressed spontaneous locomotion. The selective 5-HT(2A) antagonist MDL100907 had no effect on LY366457-induced hyperactivity, while the less selective 5-HT(2A-C) antagonist ritanserin had only a modest effect. In all cases, the doses of antagonists that reduced the locomotor response to LY366457 were greater than those previously shown to reduce the locomotor response to the psychostimulants amphetamine and cocaine and MK-801. Pretreatment with reserpine also significantly attenuated the response to LY366457, possibly implicating a monoaminergic substrate in the mediation of this effect. The phenomenonology and pharmacology of the locomotor activation induced by the mGluR antagonists differs markedly from that induced by locomotor stimulants such as amphetamine, cocaine or MK-801. These results suggest that group II mGluRs may be involved in the tonic suppression of locomotor and exploratory activity, and this suppression can be disinhibited in the presence of a group II mGluR antagonist.
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Affiliation(s)
- Michael F O'Neill
- Eli Lilly and Company Ltd, Behavioural Pharmacology, Lilly Research Centre, Erl Wood Manor, Sunninghill Rd., Windlesham, Surrey GU20 6PH, UK.
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230
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Group I metabotropic glutamate receptors in the monkey striatum: subsynaptic association with glutamatergic and dopaminergic afferents. J Neurosci 2003. [PMID: 12930805 DOI: 10.1523/jneurosci.23-20-07659.2003] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Group I metabotropic glutamate receptors (mGluRs) are involved in long-term synaptic plasticity and neuroprotection in the striatum, but the specific role(s) of mGluR1 and mGluR5 remain poorly understood. In this study, we used electron-microscopic immunocytochemistry to compare the pattern of subsynaptic and subcellular distribution of mGluR1a and mGluR5 in relation to putative glutamatergic and dopaminergic inputs to the monkey striatum. At the light-microscopic level, both group I mGluRs are expressed in the striatal neuropil. In addition, numerous perikarya of striatal output neurons are immunostained for mGluR5, but much less frequently for mGluR1a. At the electron-microscopic level, immunoreactivity for both receptor subtypes is primarily expressed postsynaptically in dendrites and spines, although presynaptic mGluR1a labeling of glutamatergic thalamostriatal boutons and, less frequently, dopaminergic and corticostriatal terminals is also seen. In contrast to mGluR1a, mGluR5 immunoreactivity is rarely encountered presynaptically. In postsynaptic elements, 40-70% of immunoreactivity for both receptor subtypes is expressed intracellularly, whereas 30-60% is apposed to the plasma membrane. More than 80% of the labeling apposed to the plasma membrane is extrasynaptic. The remaining 20% is located at the edges of putative glutamatergic synapses or in the active zone of symmetric synapses. In mGluR5-, but not mGluR1a-immunostained sections, approximately 70% of dopaminergic symmetric synapses are labeled perisynaptically. These data emphasize the differential pattern of subsynaptic localization of the two group I mGluRs and provide various presynaptic and postsynaptic sites whereby mGluR1 and mGluR5 could mediate different, but complementary, effects on glutamatergic and dopaminergic transmission in the primate striatum.
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231
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Fukumaki Y, Shibata H. Glutamate receptor genes as candidates for schizophrenia susceptibility. Drug Dev Res 2003. [DOI: 10.1002/ddr.10293] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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232
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Saransaari P, Oja SS. Characteristics of GABA release modified by glutamate receptors in mouse hippocampal slices. Neurochem Int 2003; 43:453-9. [PMID: 12742091 DOI: 10.1016/s0197-0186(03)00034-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The major part of hippocampal innervation is glutamatergic, regulated by inhibitory GABA-releasing interneurons. The modulation of [(3)H]GABA release by ionotropic and metabotropic glutamate receptors and by nitric oxide was here characterized in superfused mouse hippocampal slices. The ionotropic glutamate receptor agonists kainate, N-methyl-D-aspartate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate potentiated the basal GABA release. These effects were blocked by their respective antagonists 6-nitro-7-cyanoquinoxaline-2,3-dione (CNQX), dizocilpine and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo(f)quinoxaline-7-sulfonamide (NBQX), indicating receptor-mediated mechanisms. The NO-generating compounds S-nitroso-N-acetylpenicillamine (SNAP), sodiumnitroprusside and hydroxylamine enhanced the basal GABA release. Particularly the sodiumnitroprusside-evoked release was attenuated by the NO synthase inhibitor N(G)-nitro-L-arginine (L-NNA) and the inhibitor of soluble guanylyl cyclase 1H-(1,2,4)oxadiazolo(4,3a)quinoxalin-1-one (ODQ), indicating the involvement of the NO/cGMP pathway. This inference is corroborated by the enhancing effect of zaprinast, a phosphodiesterase inhibitor, which is known to increase cGMP levels. The K(+)-stimulated hippocampal GABA release was reduced by the groups I and III agonists of metabotropic glutamate receptors (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylate (t-ACPD) and L-(+)-2-amino-4-phosphonobutyrate (L-AP4), which effects were abolished by their respective antagonists (RS)-1-aminoindan-1,5-dicarboxylate (AIDA) and (RS)-2-cyclopropyl-4-phosphonophenylglycine (CPPG), again indicating modification by receptor-mediated mechanisms.
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Affiliation(s)
- Pirjo Saransaari
- Tampere Brain Research Center, Medical School, University of Tampere, FIN 33014 Tampere, Finland.
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233
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Salinska E, Stafiej A. Metabotropic glutamate receptors (mGluRs) are involved in early phase of memory formation: possible role of modulation of glutamate release. Neurochem Int 2003; 43:469-74. [PMID: 12742093 DOI: 10.1016/s0197-0186(03)00036-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) groups I and II are involved in the cellular processes of long-term potentiation (LTP) and learning and memory formation. I.c.v. injection of the mGluRs agonist 1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) can impair memory formation in some types of learning task. The role of mGluRs in neurotransmitters release and production of second messengers has been suggested. The aim of the present study was to determine the effect of i.c.v. administration of the new potent mGluRs agonist ABHxD-I and compare its effect with that of ACPD. We studied the effect of both agonists on acquisition and memory for a one-trial passive avoidance learning task in day-old chicks and on the training related glutamate (Glu) release. ACPD or ABHxD-I (50 nmole per chick, i.c.v. injection) were administered at different times before or after training and chicks were tested at various times after training. Chicks injected with ABHxD-I 30 min before training showed amnesia when tested 30 min or 3h after training. The amnestic effect of ACPD was significant only 30 min after training. Glu release evoked by 70 mM KCl was measured in slices prepared from the IMHV of chick brain isolated from animals injected with either ACPD or ABHxD-I 30 min before training and tested 30 min after training. Glu concentration was measured using HPLC. Both ACPD and ABHxD-I significantly increased Glu release in slices isolated from untrained chicks (30 and 48% compare to control, respectively, P<0.05). Training itself increased Glu release (41% compared to control, P<0.01) and no additional effect of either ACPD or ABHxD-I was observed. These results suggest that mGluRs groups I and II are involved in the early stages of memory formation and that application of either of the studied mGluRs agonists may interfere with that process. The amnestic effect of ABHxD-I seems to be stronger and longer lasting. Although the mechanism of this effect still remains unclear, our results suggest that disregulation of Glu release by mGluR agonists may participate in this process.
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Affiliation(s)
- Elzbieta Salinska
- Department of Neurochemistry, Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5, 02-106 Warsaw, Poland.
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234
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Flor PJ, Battaglia G, Nicoletti F, Gasparini F, Bruno V. Neuroprotective activity of metabotropic glutamate receptor ligands. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 513:197-223. [PMID: 12575822 DOI: 10.1007/978-1-4615-0123-7_7] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Metabotropic glutamate receptors form a family of currently eight subtypes (mGluR1-8), subdivided into three groups (I-III). Activation of group-II (mGluR2 and -3) or group-III metabotropic glutamate receptors (mGluR4, -6, -7 and -8) has been established to be neuroprotective in vitro and in vivo. In contrast, group-I mGluRs (mGluR1 and -5) need to be antagonized in order to evoke protection. Initially, all neuroprotective mGluR ligands were analogues of L-glutamate. Those compounds were valuable to demonstrate protection in vitro, but showed limited applicability in animal models, particularly in chronic tests, due to low blood-brain-barrier penetration. Recently, systemically active and more potent and selective ligands became available, e.g., the group-II mGluR agonists LY354740 and LY379268 or group-I antagonists like MPEP (mGluR5-selective) and BAY36-7620 (mGluR1-selective). This new generation of pharmacological agents allows a more stringent assessment of the role of individual mGluR-subtypes or groups of receptors in various nervous system disorders, including ischaemia-induced brain damage, traumatic brain injury, Huntington's and Parkinson's-like pathology or epilepsy. Moreover, the use of genetically modified animals (e.g., knock-out mice) is starting to shed light on specific functions of mGluR-subtypes in experimental neuropathologies.
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Affiliation(s)
- Peter J Flor
- Novartis PharmaAG, Nervous System Research, Basel, Switzerland
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235
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Frequency modulation of synchronized Ca2+ spikes in cultured hippocampal networks through G-protein-coupled receptors. J Neurosci 2003. [PMID: 12764103 DOI: 10.1523/jneurosci.23-10-04156.2003] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synchronized spontaneous Ca2+ spikes in networked neurons represent periodic burst firing of action potentials, which are believed to play a major role in the development and plasticity of neuronal circuitry. How these network activities are shaped and modulated by extrinsic factors during development, however, remains to be studied. Here we report that synchronized Ca2+ spikes among cultured hippocampal neurons can be modulated by two small factors that act on G-protein-coupled receptors (GPCRs): the neuropeptide PACAP (pituitary adenylate cyclase-activating polypeptide) and the chemokine SDF-1 (stromal cell-derived factor-1). PACAP effectively increases the frequency of the synchronized Ca2+ spikes when applied acutely; the PACAP potentiation of Ca2+ spikes requires the activation of the PACAP-specific PAC1 GPCRs and is mediated by the activation of cAMP signaling pathway. SDF-1, on the other hand, significantly reduces the frequency of these Ca2+ spikes through the activation of its specific GPCR CXCR4; the inhibitory action of SDF-1 is mediated by the inhibition of cAMP pathway through the Gi component of GPCRs. Taken together, these results demonstrate that synchronized neuronal network activity can be effectively modulated by physiologically and developmentally relevant small factors that act on GPCRs to target the cAMP pathway. Such modulation of neuronal activity through GPCRs may represent a significant mechanism that underlies the neuronal plasticity during neural development and functioning.
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236
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Abe H, Tateyama M, Kubo Y. Functional identification of Gd3+ binding site of metabotropic glutamate receptor 1alpha. FEBS Lett 2003; 545:233-8. [PMID: 12804782 DOI: 10.1016/s0014-5793(03)00569-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We previously reported that the metabotropic glutamate receptor1alpha (mGluR1alpha) has a sensitivity to extracellular polyvalent cations such as Ca(2+) and Gd(3+) as well as glutamate. Gd(3+) binding site was recently identified by crystal structure analysis at the interface of two subunits including Glu238, but it remains unknown whether this site is functionally involved in the activation of mGluR1alpha by Gd(3+) or not. We analyzed the ligand sensitivity of the Glu238Gln mutant, and observed that the sensitivity to extracellular Gd(3+) was completely lost, while the sensitivity to glutamate and Ca(2+) was not affected. We also observed that the presence of Gd(3+) increased the sensitivity of mGluR1alpha to glutamate, and that this effect was again lost by Glu238Gln mutation. These results suggest that the binding of Gd(3+) or a related endogenous substance to this site, alone or in cooperation with glutamate binding at a distant site, leads mGluR1alpha to activation.
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Affiliation(s)
- Hideki Abe
- Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Graduate School and Faculty of Medicine, D-566, 1-5-45 Yushima, Bunkyo, Tokyo 113-8519, Japan
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237
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Nagase T, Ito KI, Kato K, Kaneko K, Kohda K, Matsumoto M, Hoshino A, Inoue T, Fujii S, Kato H, Mikoshiba K. Long-term potentiation and long-term depression in hippocampal CA1 neurons of mice lacking the IP(3) type 1 receptor. Neuroscience 2003; 117:821-30. [PMID: 12654335 DOI: 10.1016/s0306-4522(02)00803-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
To investigate the role in synaptic plasticity of Ca(2+) released from intracellular Ca(2+) stores, mice lacking the inositol 1,4,5-trisphosphate type 1 receptor were developed and the physiological properties, long-term potentiation, and long-term depression of their hippocampal CA1 neurons were examined. There were no significant differences in basic synaptic functions, such as membrane properties and the input/output relationship, between homozygote mutant and wild-type mice. Enhanced paired-pulse facilitation at interpulse intervals of less than 60 ms and enhanced post-tetanic potentiation were observed in the mutant mice, suggesting that the presynaptic mechanism was altered by the absence of the inositol 1,4,5-trisphosphate type 1 receptor. Long-term potentiation in the field-excitatory postsynaptic potentials induced by tetanus (100 Hz, 1 s) and the excitatory postsynaptic currents induced by paired stimulation in hippocampal CA1 pyramidal neurons under whole-cell clamp conditions were significantly greater in mutant mice than in wild-type mice. Homosynaptic long-term depression of CA1 synaptic responses induced by low-frequency stimulation (1 Hz, 500 pulses) was not significantly different, but heterosynaptic depression of the non-associated pathway induced by tetanus was blocked in the mutant mice. Both long-term potentiation and long-term depression in mutant mice were completely dependent on N-methyl-D-aspartate receptor activity. To rule out the possibility of an effect compensating for the lack of the inositol 1,4,5-trisphosphate type 1 receptor occurring during development, an anti-inositol 1,4,5-trisphosphate type 1 receptor monoclonal antibody that blocks receptor function was diffused into the wild-type cell through a patch pipette, and the effect of acute block of inositol 1,4,5-trisphosphate type 1 receptor on long-term potentiation was examined. Significant enhancement of long-term potentiation was observed compared with after control immunoglobulin G injection, suggesting that developmental redundancy was not responsible for the increase in long-term potentiation amplitude observed in the mutant mouse. The properties of channels that could be involved in long-term potentiation induction were examined using whole-cell recording. N-methyl-D-aspartate currents were significantly larger in mutant mice than in wild-type mice only between holding potentials of -60 and -80 mV. We conclude that inositol 1,4,5-trisphosphate type 1 receptor activity is not essential for the induction of synaptic plasticity in hippocampal CA1 neurons, but appears to negatively regulate long-term potentiation induction by mild modulation of channel activities.
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Affiliation(s)
- T Nagase
- Department of Physiology, Yamagata University School of Medicine, 990-9585, Yamagata, Japan
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238
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Cryan JF, Kelly PH, Neijt HC, Sansig G, Flor PJ, van Der Putten H. Antidepressant and anxiolytic-like effects in mice lacking the group III metabotropic glutamate receptor mGluR7. Eur J Neurosci 2003; 17:2409-17. [PMID: 12814372 DOI: 10.1046/j.1460-9568.2003.02667.x] [Citation(s) in RCA: 211] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Glutamatergic neurotransmission has been strongly implicated in the pathophysiology of affective disorders, such as major depression and anxiety. Of all glutamate receptors, the role of group III metabotropic glutamate receptors (mGluR4, mGluR6, mGluR7, mGluR8) in such disorders is the least investigated because of the lack of specific pharmacological tools. To this end, we examined the behavioural profiles of mice with a targeted deletion of the gene for mGluR7 (mGluR7-/-) in animal models of depression and anxiety. mGluR7-/- mice were compared with wild-type (mGluR7+/+) littermates and showed substantially less behavioural immobility in both the forced swim test and the tail suspension test. Both behavioural paradigms are widely used to predict antidepressant-like activity. Further, mGluR7-/- mice displayed anxiolytic activity in four different behavioural tests, i.e. the light-dark box, the elevated plus maze, the staircase test, and the stress-induced hyperthermia test, while their cognitive performance was normal in the passive avoidance paradigm. Analysis of locomotor activity in a novel environment demonstrated that mGluR7-/- mice were slightly more active in the initial minutes following placement in the chamber only. Together, these data suggest that mGluR7 may play a pivotal role in mechanisms that regulate behavioural responses to aversive states. Therefore, drugs acting at mGluR7 may provide novel treatments for psychiatric disorders such as depression and anxiety.
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Affiliation(s)
- John F Cryan
- Nervous System Research, Novartis Institutes for BioMedical Sciences, Novartis Pharma AG, Basel, Switzerland.
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239
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Abe H, Misaka T, Tateyama M, Kubo Y. Effects of coexpression with Homer isoforms on the function of metabotropic glutamate receptor 1alpha. Mol Cell Neurosci 2003; 23:157-68. [PMID: 12812750 DOI: 10.1016/s1044-7431(03)00052-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
We previously showed that the metabotropic glutamate receptor 1alpha (mGluR1alpha) has a sensitivity to extracellular polyvalent cations such as Ca(2+) and Gd(3+) as well as glutamate. Here we show that mGluR1alpha-mediated responses to these ligands are modulated by the scaffold protein Homer. When HEK293 cells were transiently cotransfected with Homer 1c and mGluR1alpha, the maximum rate of rise and amplitude of glutamate-evoked [Ca(2+)](i) transients were increased and there was a rightward shift in the concentration-response relationship. The response of mGluR1alpha to abrupt increases in [Gd(3+)](o) was characteristic in that the concentration-response relationship was bell-shaped and Homer 1c broadened the effective range at both low and high concentrations. The effects of Homer 1a, which lacks clustering effect, differed qualitatively from those of Homer 1c. The effects of both Homer 1c and 1a on mGluR1alpha were decreased significantly in mGluR1alpha P1147E mutant which lacks the affinity to Homer, showing that the effects were mediated by binding to mGluR1alpha. Taken together, the binding of Homer 1c to mGluR1alpha was shown to cause not only an efficient link to Ca(2+)-store and a decrease in the surface expression, but also qualitative changes of the ligand-sensing function in a ligand type-specific manner.
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Affiliation(s)
- Hideki Abe
- Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Graduate School and Faculty of Medicine, Bunkyo, Tokyo, Japan, 113-8519
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240
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Higashida H, Zhang JS, Mochida S, Chen XL, Shin Y, Noda M, Hossain KZ, Hoshi N, Hashii M, Shigemoto R, Nakanishi S, Fukuda Y, Yokoyama S. Subtype-specific coupling with ADP-ribosyl cyclase of metabotropic glutamate receptors in retina, cervical superior ganglion and NG108-15 cells. J Neurochem 2003; 85:1148-58. [PMID: 12753074 DOI: 10.1046/j.1471-4159.2003.01751.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cyclic ADP-ribose (cADP-ribose) is a putative second messenger or modulator. However, the role of cADP-ribose in the downstream signals of the metabotropic glutamate receptors (mGluRs) is unclear. Here, we show that glutamate stimulates ADP-ribosyl cyclase activity in rat or mouse crude membranes of retina via group III mGluRs or in superior cervical ganglion via group I mGluRs. The retina of mGluR6-deficient mice showed no increase in the ADP-ribosyl cyclase level in response to glutamate. GTP enhanced the initial rate of basal and glutamate-stimulated cyclase activity. GTP-gamma-S also stimulated basal activity. To determine whether the coupling mode of mGluRs to ADP-ribosyl cyclase is a feature common to individual cloned mGluRs, we expressed each mGluR subtype in NG108-15 neuroblastoma x glioma hybrid cells. The glutamate-induced stimulation of the cyclase occurs preferentially in NG108-15 cells over-expressing mGluRs1, 3, 5, and 6. Cells expressing mGluR2 or mGluRs4 and 7 exhibit inhibition or no coupling, respectively. Glutamate-induced activation or inhibition of the cyclase activity was eliminated after pre-treatment with cholera or pertussis toxin, respectively. Thus, the subtype-specific coupling of mGluRs to ADP-ribosyl cyclase via G proteins suggests that some glutamate-evoked neuronal functions are mediated by cADP-ribose.
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Affiliation(s)
- Haruhiro Higashida
- Department of Biophysical Genetics, Kanazawa University Graduate School of Medicine, Kanazawa, Japan.
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241
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Aronica E, Gorter JA, Ijlst-Keizers H, Rozemuller AJ, Yankaya B, Leenstra S, Troost D. Expression and functional role of mGluR3 and mGluR5 in human astrocytes and glioma cells: opposite regulation of glutamate transporter proteins. Eur J Neurosci 2003; 17:2106-18. [PMID: 12786977 DOI: 10.1046/j.1460-9568.2003.02657.x] [Citation(s) in RCA: 226] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We examined the regulation of glutamate transporter protein expression after stimulation with selective metabotropic glutamate receptor (mGluR) agonists in cultured human glial cells. mGluR3 and mGluR5 are expressed in human astrocytes and in human glioma cells in vivo as well as in vitro, as shown by either RT-PCR or western blot analysis. The selective group I agonist (S)-3,5-dihydroxyphenylglycine produced a significant down-regulation of both GLAST and GLT-1 protein expression in astrocytes cultured in the presence of growth factors. This condition mimics the morphology of reactive glial cells in vivo including an increased expression of mGluR5 protein (observed in pathological conditions). In contrast, (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine, a selective agonist of group II metabotropic glutamate receptors, positively modulates the expression of GLAST and GLT-1 proteins. A similar opposite effect of (S)-3,5-dihydroxyphenylglycine and (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine was observed for the expression of EAAT3 protein in U373 glioblastoma cell line. Selective group I and II antagonists prevented these effects. Pharmacological inhibition of mitogen-activated protein kinase and phosphatidylinositol-3-K pathways reduces the induction of GLT-1 observed in response to the group II metabotropic glutamate receptor agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine. Thus, mGluR3 and mGluR5 can critically and differentially modulate the expression of glutamate transporters and may represent interesting pharmacological targets to regulate the extracellular levels of glutamate in pathological conditions.
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Affiliation(s)
- Eleonora Aronica
- Department of (Neuro)Pathology, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
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242
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Kammermeier PJ, Ikeda SR. A role for Seven in Absentia Homolog (Siah1a) in metabotropic glutamate receptor signaling. BMC Neurosci 2003; 2:15. [PMID: 11686852 PMCID: PMC58838 DOI: 10.1186/1471-2202-2-15] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2001] [Accepted: 10/08/2001] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND The mammalian homologue of Seven in Absentia (Siah) can act in the ubiquitin/proteasome pathway. Recent work has shown that Siah can bind group I metabotropic glutamate receptors (mGluRs), but the functional consequences of this interaction are unknown. RESULTS The effects of coexpression of Siah on group I mGluR signaling were examined using heterologous expression in rat sympathetic, superior cervical ganglion neurons. Siah1a attenuated heterologously expressed group I mGluR-mediated calcium current inhibition, but was without effect on group II mGluR- or NE-mediated calcium current modulation via heterologously expressed mGluR2 or native a2 adrenergic receptors, respectively, indicating that the effect of Siah was specific for group I mGluRs. Surface expression and subcellular distribution of group I mGluRs were not detectably altered in the presence of Siah1a as assessed by immunoflourescence experiments with epitope tagged receptors and imaging of a GFP/mGluR fusion construct. In addition, an N-terminal Siah deletion construct, which cannot function in the proteolysis pathway, displayed effects similar to the wild type Siah1a. Finally, coexpression of calmodulin, which competes with Siah1a for binding to the C-terminal tail of group I mGluRs, reversed the effect of Siah1a on mGluR-mediated signaling. CONCLUSIONS These data supported the conclusion that the attenuation of mGluR signaling induced by Siah1a expression was likely a direct consequence of Siah/mGluR association rather than a result of targeting of the receptors to the proteosome. In addition, the data suggest that the binding of CaM and Siah may play an important role in the regulation of group I mGluR function.
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Affiliation(s)
- Paul J Kammermeier
- Laboratory of Molecular Physiology, Guthrie Research Institute, Sayre, PA 18840, USA
| | - Stephen R Ikeda
- Laboratory of Molecular Physiology, Guthrie Research Institute, Sayre, PA 18840, USA
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243
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Iacovelli L, Salvatore L, Capobianco L, Picascia A, Barletta E, Storto M, Mariggiò S, Sallese M, Porcellini A, Nicoletti F, De Blasi A. Role of G protein-coupled receptor kinase 4 and beta-arrestin 1 in agonist-stimulated metabotropic glutamate receptor 1 internalization and activation of mitogen-activated protein kinases. J Biol Chem 2003; 278:12433-42. [PMID: 12519791 DOI: 10.1074/jbc.m203992200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The metabotropic glutamate 1 (mGlu(1)) receptor in cerebellar Purkinje cells plays a key role in motor learning and motor coordination. Here we show that the G protein-coupled receptor kinases (GRK) 2 and 4, which are expressed in these cells, regulate the mGlu(1) receptor by at least in part different mechanisms. Using kinase-dead mutants in HEK293 cells, we found that GRK4, but not GRK2, needs the intact kinase activity to desensitize the mGlu(1) receptor, whereas GRK2, but not GRK4, can interact with and regulate directly the activated Galpha(q). In cells transfected with GRK4 and exposed to agonist, beta-arrestin was first recruited to plasma membranes, where it was co-localized with the mGlu(1) receptor, and then internalized in vesicles. The receptor was also internalized but in different vesicles. The expression of beta-arrestin V53D dominant negative mutant, which did not affect the mGlu(1) receptor internalization, reduced by 70-80% the stimulation of mitogen-activated protein (MAP) kinase activation by the mGlu(1) receptor. The agonist-stimulated differential sorting of the mGlu(1) receptor and beta-arrestin as well as the activation of MAP kinases by mGlu(1) agonist was confirmed in cultured cerebellar Purkinje cells. A major involvement of GRK4 and of beta-arrestin in agonist-dependent receptor internalization and MAP kinase activation, respectively, was documented in cerebellar Purkinje cells using an antisense treatment to knock down GRK4 and expressing beta-arrestin V53D dominant negative mutant by an adenovirus vector. We conclude that GRK2 and GRK4 regulate the mGlu(1) receptor by different mechanisms and that beta-arrestin is directly involved in glutamate-stimulated MAP kinase activation by acting as a signaling molecule.
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Affiliation(s)
- Luisa Iacovelli
- Istituto Neurologico Mediterraneo Neuromed, Istituto di Ricovero e Cura a Carattere Scientifico, 86077 Pozzilli, Italy
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244
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Scaccianoce S, Matrisciano F, Del Bianco P, Caricasole A, Di Giorgi Gerevini V, Cappuccio I, Melchiorri D, Battaglia G, Nicoletti F. Endogenous activation of group-II metabotropic glutamate receptors inhibits the hypothalamic-pituitary-adrenocortical axis. Neuropharmacology 2003; 44:555-61. [PMID: 12668041 DOI: 10.1016/s0028-3908(03)00027-3] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Systemic injection of the mGlu2/3 receptor antagonist, LY341495 (1 mg/kg, i.p.), increased plasma corticosterone in mice to an extent similar to that induced by the despair test. Treatment with the mGlu2/3 receptor agonist, LY379268 (1 mg/kg, i.p.), or the non-competitive mGlu5 receptor antagonist, MPEP (5 mg/kg, i.p.), failed to induce significant changes in corticosterone levels. Searching for a site of action of LY341495, we examined the expression of mGlu receptor subtypes in the various anatomical regions of the mouse hypothalamic-pituitary-adrenal (HPA) axis. Only mGlu5 and -7 receptor mRNAs were detected in the adrenal gland by RT-PCR, whereas mGlu -1, -3, -4, -5, -7 and -8 receptor mRNAs were detected in the anterior pituitary. All transcripts (with the exception of mGlu5 and mGlu6 receptor mRNAs) were detected in the hypothalamus. However, Western blot analysis showed the presence of mGlu2/3 receptor proteins only in the hypothalamus and not in the anterior pituitary. This was consistent with functional data showing that LY341495 (0.1 and 1 microM) failed to affect ACTH secretion from isolated mouse anterior pituitaries. Moving from these observations, we examined whether LY341495 could activate the HPA axis by inhibiting mGlu2/3 receptors at hypothalamic level. We measured the release of corticotropin releasing hormone (CRH) in isolated mouse hypothalami incubated in the presence of subtype-selective mGlu receptor agonists or antagonists. Among all the drugs we have tested, only LY341495 was able to increase CRH secretion. With high concentrations of LY341495 (1 microM) this increase was similar to that induced by 50 mM K(+). The action of LY341495 was prevented by the combined application of the mGlu2/3 receptor agonist, LY379268. We conclude that group-II mGlu receptors tonically regulate the HPA axis by controlling CRH secretion at hypothalamic level.
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Affiliation(s)
- S Scaccianoce
- Department of Human Physiology and Pharmacology, University of Rome La Sapienza, Ple A. Moro 5, Italy
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245
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Stover JF, Sakowitz OW, Beyer TF, Dohse NK, Kroppenstedt SN, Thomale UW, Schaser KD, Unterberg AW. Effects of LY379268, a selective group II metabotropic glutamate receptor agonist on EEG activity, cortical perfusion, tissue damage, and cortical glutamate, glucose, and lactate levels in brain-injured rats. J Neurotrauma 2003; 20:315-26. [PMID: 12866811 DOI: 10.1089/089771503765172273] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Activating presynaptic group II metabotropic glutamate (mGlu II) receptors reduces synaptic glutamate release. Attenuating glutamatergic transmission without blocking ionotropic glutamate receptors, thus avoiding unfavorable psychomimetic side effects, makes mGlu II receptor agonists a promising target in treating brain-injured patients. Neuroprotective effects of LY379268 were investigated in rats following controlled cortical impact injury (CCI). At 30 min after CCI, rats received a single intraperitoneal injection of LY379268 (10 mg/kg/body weight) or NaCl. Changes in EEG activity and pericontusional cortical perfusion were determined before trauma, at 4, 24, and 48 h, and 7 days after CCI. Brain edema and contusion volume were determined at 24 h and 7 days after CCI, respectively. Before brain removal pericontusional cortical glutamate, glucose, and lactate were measured via microdialysis. During the early period following CCI, EEG activity and cortical perfusion were significantly reduced in rats receiving LY379268. At 7 days, cortical perfusion was significantly increased in rats treated with LY379268, while EEG activity was depressed as in control rats. While brain edema remained unchanged at 24 h, cortical contusion was significantly decreased by 56% at 7 days after CCI. Cortical glutamate, glucose, and lactate were not influenced. Significant reductions in EEG activity and contusion volume by LY379268 do not appear mediated by attenuated excitotoxicity and energetic impairment. Overall, an additional decrease in cortical perfusion seems to interfere with the anti-edematous potential of LY379268 during the early period following CCI, while an increase in perfusion in LY379268-treated rats at 7 days might contribute to tissue protection.
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Affiliation(s)
- John F Stover
- Department of Neurosurgery, Charité-Virchow Medical Center, Humboldt-University Berlin, Berlin, Germany.
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246
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Defagot MC, Villar MJ, Antonelli MC. Differential localization of metabotropic glutamate receptors during postnatal development. Dev Neurosci 2003; 24:272-82. [PMID: 12457065 DOI: 10.1159/000066741] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The localization of metabotropic glutamate receptors (mGluRs) during development has been associated with brain maturation and plasticity. The developmental immunohistochemical analysis of mGluR1alpha, mGluR2/3 and mGluR4a expression was performed in the cerebral cortex, hippocampus and basal ganglia at postnatal days (P) 4, 8, 12, 35 and 60. In early stages (P4 and P8) mGluR1alpha-like immunoreactivity (mGluR1alpha-LI) was detected in cell bodies and fibers of the frontal cortex, hippocampus and globus pallidus. At P35 and P60, the staining was observed in pyramidal cells and fibers in the deepest layers of the cortex and in stratum oriens of the hippocampus, while a lower labeling was observed in fibers of the globus pallidus. No immunostaining was observed in substantia nigra pars reticulata until P12, when a dense network of fiber staining was detected through the adult stages (P35, P60). mGluR2/3-LI was present from the second week of development in fibers and cell bodies of the stratum lacunosum moleculare of the CA1-CA3 and striatum; this staining pattern persisted until adult stages. mGluR4a-LI was observed at P12 in neuronal bodies of the cortex, in pyramidal cells of the hippocampus and in neuronal cells of the striatum. At P35 and P60, a strong signal was observed in a reduced number of labeled cells of the cerebral cortex, in fibers of the stratum oriens of CA1 and in long processes of substantia nigra pars reticulata. Our results indicate that there are significant changes in the protein expression of mGluR subunits through postnatal development. These differences may play a significant role in the establishment of proper synaptic circuitry in early postnatal life, as well as contributing to the maintenance, stabilization, and plasticity of the rat forebrain, particularly through the participation of mGluR1alpha and mGluR4a.
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Affiliation(s)
- María C Defagot
- Facultad de Ciencias Biomédicas, Universidad Austral, Buenos Aires, Argentina.
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Malherbe P, Kratochwil N, Knoflach F, Zenner MT, Kew JNC, Kratzeisen C, Maerki HP, Adam G, Mutel V. Mutational analysis and molecular modeling of the allosteric binding site of a novel, selective, noncompetitive antagonist of the metabotropic glutamate 1 receptor. J Biol Chem 2003; 278:8340-7. [PMID: 12509432 DOI: 10.1074/jbc.m211759200] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A model of the rmGlu1 seven-transmembrane domain complexed with a negative allosteric modulator, 1-ethyl-2-methyl-6-oxo-4-(1,2,4,5-tetrahydro-benzo[d]azepin-3-yl)- 1,6-dihydro-pyrimidine-5-carbonitrile (EM-TBPC) was constructed. Although the mGlu receptors belong to the family 3 G-protein-coupled receptors with a low primary sequence similarity to rhodopsin-like receptors, the high resolution crystal structure of rhodopsin was successfully applied as a template in this model and used to select residues for site-directed mutagenesis. Three mutations, F801(6.51)A, Y805(6.55)A, and T815(7.39)M caused complete loss of the [(3)H]EM-TBPC binding and blocked the EM-TBPC-mediated inhibition of glutamate-evoked G-protein-coupled inwardly rectifying K(+) channel current and [Ca(2+)](i) response. The mutation W798(6.48)F increased the binding affinity of antagonist by 10-fold and also resulted in a marked decrease in the IC(50) value (4 versus 128 nm) compared with wild type. The V757(5.47)L mutation led to a dramatic reduction in binding affinity by 13-fold and a large increase in the IC(50) value (1160 versus 128 nm). Two mutations, N7474(5.51)A and N7504(5.54)A, increased the efficacy of the EM-TBPC block of the glutamate-evoked [Ca(2+)](i) response. We observed a striking conservation in the position of critical residues. The residues Val-757(5.47), Trp-798(6.48), Phe-801(6.51), Tyr-805(6.55), and Thr-815(7.39) are critical determinants of the EM-TBPC-binding pocket of the mGlu1 receptor, validating the rhodopsin crystal structure as a template for the family 3 G-protein-coupled receptors. In our model, the aromatic ring of EM-TBPC might interact with the cluster of aromatic residues formed from Trp-798(6.48), Phe-801(6.51), and Tyr-805(6.55), thereby blocking the movement of the TM6 helix, which is crucial for receptor activation.
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Affiliation(s)
- Pari Malherbe
- Pharma Division, Discovery Research CNS and Chemistry, F. Hoffmann-La Roche Ltd., CH-4070 Basel, Switzerland.
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248
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Folbergrová J, Haugvicová R, Mares P. Seizures induced by homocysteic acid in immature rats are prevented by group III metabotropic glutamate receptoragonist (R,S)-4-phosphonophenylglycine. Exp Neurol 2003; 180:46-54. [PMID: 12668148 DOI: 10.1016/s0014-4886(02)00047-x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The potential anticonvulsant effect of group III metabotropic glutamate receptor (mGluR) agonist (R,S)-4-phosphonophenylglycine ((R,S)-PPG) against seizures induced in immature 12-day-old rats by bilateral intracerebroventricular (icv) infusion of DL-homocysteic acid (DL-HCA, 600 nmol/side) was examined in the present study. Rat pups were sacrificed during generalized clonic-tonic seizures, approximately 45 to 50 min after infusion. Comparable time intervals were used for sacrificing the pups which had received (R,S)-PPG. Low doses of (R,S)-PPG (10 nmol, icv) provided a pronounced anticonvulsant effect which was abolished by pretreatment with a selective group III mGluR antagonist (R,S)-alpha-methylserine-O-phosphate. Generalized clonic-tonic seizures were completely suppressed and cortical energy metabolite changes which normally accompany these seizures were either normalized (glucose and glycogen decreases) or markedly ameliorated (an accumulation of lactate). Despite the absence of obvious motor phenomena, EEG recordings revealed sporadic ictal activity, mostly in the dorsal hippocampus. Spreading of this activity into the frontal cortex was rather exceptional. The latency of ictal EEG in pretreated rats was significantly prolonged. Our data suggest that the predominant effect of (R,S)-PPG might concern seizure spread. The administration of (R,S)-PPG alone did not cause any overt behavioral side effects; it did not change the EEG pattern and did not influence cortical metabolite levels, with the exception of increased concentrations of glucose. The present findings suggest that group III mGlu receptor agonists may be of therapeutic significance for treating childhood epilepsies.
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Affiliation(s)
- Jaroslava Folbergrová
- Institute of Physiology, Academy of Sciences of the Czech Republic, Vídenská 1083, 142 20 Prague 4, Czech Republic.
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249
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Shahraki A, Stone TW. Interactions between adenosine and metabotropic glutamate receptors in the rat hippocampal slice. Br J Pharmacol 2003; 138:1059-68. [PMID: 12684261 PMCID: PMC1573745 DOI: 10.1038/sj.bjp.0705083] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. We have examined excitatory postsynaptic potentials and paired-pulse interactions in rat hippocampal slices to obtain more information about the site and mechanism of interactions between metabotropic glutamate receptors and adenosine receptors. 2. The results show that the suppression of adenosine sensitivity is explained by a selectively reduced responsiveness to A(1) receptor stimulation, and does not involve any facilitation of A(2A) adenosine receptors, since it can be obtained in the absence of endogenous adenosine and is not prevented by the A(2A) receptor blocker ZM241385. 3. The glutamate receptors involved are of the group I class since the suppression of adenosine sensitivity is produced by ACPD and the group I selective compound DHPG. Furthermore, the effects of DHPG could be prevented by LY367385, a selective antagonist at the mGlu(1a) subtype of group I receptors. The selective antagonist at mGlu(5) receptors, SIB1893, did not prevent the suppression of adenosine sensitivity by DHPG. Blockade of the DHPG/adenosine interaction was also obtained by superfusion with the protein kinasae C inhibitor chelerythrine. 4. Since the suppression of adenosine responses by metabotropic receptor agonists was seen in the paired-pulse paradigm, we conclude that the observed interactions occur at the level of the presynaptic terminals. 5. The interaction with adenosine receptors is not specific, but applies also to a suppression of responses mediated by the GABA(B) receptor agonist baclofen. 6. We conclude that activation of the mGlu1a subtype of receptor can suppress responses mediated via adenosine A1 receptors, probably by activating protein kinase C. Since the changes induced by metabotropic glutamate receptor agonists last for at least 60 min, the data also imply that these interactions could play an important role in changes of synaptic function long after even transient increases of glutamate release in the CNS.
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Affiliation(s)
- Ali Shahraki
- Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ
| | - Trevor W Stone
- Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ
- Author for correspondence:
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de Novellis V, Marabese I, Palazzo E, Rossi F, Berrino L, Rodella L, Bianchi R, Rossi F, Maione S. Group I metabotropic glutamate receptors modulate glutamate and gamma-aminobutyric acid release in the periaqueductal grey of rats. Eur J Pharmacol 2003; 462:73-81. [PMID: 12591098 DOI: 10.1016/s0014-2999(03)01342-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In this study, we investigated the effects of group I metabotropic glutamate (mglu) receptor ligands on glutamate and gamma-aminobutyric acid (GABA) extracellular concentrations at the periaqueductal grey level by using in vivo microdialysis. An agonist of group I mglu receptors, (S)-3,5-dihydroxyphenylglycine [(S)-3,5-DHPG, 1 and 2 mM], as well as a selective agonist of mglu(5) receptors, (RS)-2-chloro-5-hydroxyphenylglycine (CHPG, 2 and 4 mM), both increased dialysate glutamate and GABA concentrations. 7-(Hydroxyimino)cyclopropa-[b]-chromen-1alpha-carboxylate ethyl ester (CPCCOEt, 1 mM), a selective mglu(1) receptor antagonist, and 2-methyl-6-(phenylethynyl)pyridine (MPEP, 0.5 mM), a selective mglu(5) receptor antagonist, perfused in combination with DHPG, antagonized the effect induced by DHPG on the extracellular glutamate and GABA concentrations. MPEP (0.5 mM), perfused in combination with CHPG, antagonized the increased glutamate and GABA extracellular levels induced by CHPG. MPEP (1 mM) decreased the extracellular concentrations of glutamate but did not modify the dialysate GABA concentrations. Moreover, as the intra-periaqueductal grey perfusion of (RS)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid [(RS)-CPP, 100 microM], a selective N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, did not change the extracellular concentrations of glutamate, this suggests that the MPEP-induced decrease in glutamate is not a consequence of NMDA receptor blockade. These data show that group I mglu receptors in the periaqueductal grey may modulate the release of glutamate and GABA in awake, freely moving rats. In particular, mglu(5), but not mglu(1), receptors seem to be functionally active on glutamate terminals.
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Affiliation(s)
- Vito de Novellis
- Department of Experimental Medicine, Section of Pharmacology L. Donatelli, Faculty of Medicine and Surgery, Second University of Naples, Via Costantinopoli, 16 80138 Naples, Italy.
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