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Nishitani A, Nagayoshi H, Takenaka S, Asano M, Shimizu S, Ohno Y, Kuramoto T. Involvement of NMDA receptors in tremor expression in Aspa/Hcn1 double-knockout rats. Exp Anim 2020; 69:388-394. [PMID: 32507787 PMCID: PMC7677080 DOI: 10.1538/expanim.20-0025] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We recently demonstrated that aspartoacylase (Aspa) and
hyperpolarization-activated cyclic nucleotide-gated potassium channel 1
(Hcn1) genes were causative of essential tremor (ET) in rats. This
finding was obtained using
Aspaem34Kyo/Hcn1A354V
double-mutant rats, but they were bred on a heterogeneous genetic background of two
strains, F344 and WTC. Here, we developed an
Aspaem34Kyo/Hcn1em1Kyo
double-knockout rat strain with a homogenous F344 genetic background and studied the
ability of glutamate receptor antagonists to suppress ET. The
F344-Aspa/Hcn1 double-knockout rats exhibited
spontaneous, intense body tremor equivalent to that in the double-mutant rats.
N-acetyl-aspartate (NAA), a substrate of ASPA, showed accumulation in
all brain regions and in the spinal cord. However,
N-acetyl-aspartyl-glutamate (NAAG), which is derived from NAA and
interacts with glutamatergic receptors, was decreased in the medulla oblongata of the
double-knockout rats. The tremor was suppressed by
3-[(R)-2-carboxypiperazin-4-yl]-prop-2-enyl-1-phosphonic acid, an
N-methyl-D-aspartate (NMDA) receptor antagonist, in
F344-Aspa/Hcn1 double-knockout rats. The non-NMDA
glutamate receptor antagonist NBQX weakly inhibited the tremor, while the metabotropic
glutamate receptor antagonist LY341495 showed no effect. In addition, both NR2B
subunit-specific (Ro 25-6981) and NR2C/NR2D subunit-specific (cis-piperidine dicarboxylic
acid) NMDA receptor antagonists suppressed the tremor. These data indicated that the
pathogenesis of tremor in Aspa/Hcn1 double-knockout rats
involved ionotropic glutamate receptors, particularly NMDA receptors.
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Affiliation(s)
- Ai Nishitani
- Institute of Laboratory Animals, Graduate School of Medicine, Kyoto University, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Haruna Nagayoshi
- Osaka Institute of Public Health, 1-3-69 Nakamichi, Higashinari-ku, Osaka 537-0025, Japan
| | - Shigeo Takenaka
- Department of Clinical Nutrition, Graduate School of Comprehensive Rehabilitation, Osaka Prefecture University, 3-7-30 Habikino, Osaka 583-8555, Japan
| | - Masahide Asano
- Institute of Laboratory Animals, Graduate School of Medicine, Kyoto University, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Saki Shimizu
- Department of Pharmacology, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan
| | - Yukihiro Ohno
- Department of Pharmacology, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan
| | - Takashi Kuramoto
- Institute of Laboratory Animals, Graduate School of Medicine, Kyoto University, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.,Department of Animal Science, Faculty of Agriculture, Tokyo University of Agriculture, 1737 Funako, Atsugi, Kanagawa 243-0034, Japan
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Tang J, O’Neill J, Alger JR, Shen Z, Johnson MC, London ED. N-Acetyl and Glutamatergic Neurometabolites in Perisylvian Brain Regions of Methamphetamine Users. Int J Neuropsychopharmacol 2019; 22:1-9. [PMID: 29788422 PMCID: PMC6313110 DOI: 10.1093/ijnp/pyy042] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Revised: 03/21/2018] [Accepted: 05/15/2018] [Indexed: 02/05/2023] Open
Abstract
Background Methamphetamine induces neuronal N-acetyl-aspartate synthesis in preclinical studies. In a preliminary human proton magnetic resonance spectroscopic imaging investigation, we also observed that N-acetyl-aspartate+N-acetyl-aspartyl-glutamate in right inferior frontal cortex correlated with years of heavy methamphetamine abuse. In the same brain region, glutamate+glutamine is lower in methamphetamine users than in controls and is negatively correlated with depression. N-acetyl and glutamatergic neurochemistries therefore merit further investigation in methamphetamine abuse and the associated mood symptoms. Methods Magnetic resonance spectroscopic imaging was used to measure N-acetyl-aspartate+N-acetyl-aspartyl-glutamate and glutamate+glutamine in bilateral inferior frontal cortex and insula, a neighboring perisylvian region affected by methamphetamine, of 45 abstinent methamphetamine-dependent and 45 healthy control participants. Regional neurometabolite levels were tested for group differences and associations with duration of heavy methamphetamine use, depressive symptoms, and state anxiety. Results In right inferior frontal cortex, N-acetyl-aspartate+N-acetyl-aspartyl-glutamate correlated with years of heavy methamphetamine use (r = +0.45); glutamate+glutamine was lower in methamphetamine users than in controls (9.3%) and correlated negatively with depressive symptoms (r = -0.44). In left insula, N-acetyl-aspartate+N-acetyl-aspartyl-glutamate was 9.1% higher in methamphetamine users than controls. In right insula, glutamate+glutamine was 12.3% lower in methamphetamine users than controls and correlated negatively with depressive symptoms (r = -0.51) and state anxiety (r = -0.47). Conclusions The inferior frontal cortex and insula show methamphetamine-related abnormalities, consistent with prior observations of increased cortical N-acetyl-aspartate in methamphetamine-exposed animal models and associations between cortical glutamate and mood in human methamphetamine users.
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Affiliation(s)
- Jinsong Tang
- Laboratory of Molecular Neuroimaging, Semel Institute for Neuroscience and Human Behavior and Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, California
- Second Xiangya Hospital, Central South University, Changsha, China
| | - Joseph O’Neill
- Division of Child and Adolescent Psychiatry, Semel Institute for Neuroscience and Human Behavior and Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, California
| | | | - Zhiwei Shen
- The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Maritza C Johnson
- Laboratory of Molecular Neuroimaging, Semel Institute for Neuroscience and Human Behavior and Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, California
| | - Edythe D London
- Laboratory of Molecular Neuroimaging, Semel Institute for Neuroscience and Human Behavior and Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, California
- Department of Molecular and Medical Pharmacology, University of California, Los Angeles, California
- Brain Research Institute, University of California, Los Angeles, California
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Khacho P, Wang B, Bergeron R. The Good and Bad Sides of NAAG. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2016; 76:311-49. [PMID: 27288081 DOI: 10.1016/bs.apha.2016.01.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Why has such a small peptide been the source of controversy in neuroscience over the last 5 decades? Is N-acetyl-aspartyl-glutamate (NAAG) a neurotransmitter? Is NAAG located in neuronal tissue or in astrocytes? Is NAAG involved in neuropsychiatric and neurodegenerative disorders? Is NAAG therapeutically beneficial in the treatment of stroke or in initiating cascades of events leading to psychosis? After many years of intense research there is no clear consensus within the scientific community on how NAAG behaves in the brain. One of the major controversies about NAAG is its physiological action at N-methyl-d-aspartate (NMDA) receptors. While some researchers strongly argue that NAAG acts as a weak agonist at NMDA receptors, others have suggested that NAAG could behave as a potent antagonist. Published data from our laboratory demonstrate that the effect of NAAG on NMDA receptors could be influenced by a number of factors including the subcellular localization and subunit composition of NMDA receptors, as well as protons. In this chapter, we will summarize the knowledge of the literature on NAAG, however, we will place emphasis on our recently published data. More specifically, we have reported interesting findings on the effects of NAAG on NMDA receptors at synaptic and extrasynaptic sites using a pharmacological paradigm to distinguish the two populations of NMDA receptors. Additionally, we have evaluated the role of NAAG on GluN2A- and GluN2B-containing NMDA receptors using a HEK293 cell recombinant system. Finally, we have studied the effects of NAAG on GluN2A- and GluN2B-containing NMDA receptors in different extracellular pH conditions. We believe that our findings could potentially resolve some aspects of the debate regarding the role of NAAG at NMDA receptors.
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Affiliation(s)
- P Khacho
- University of Ottawa, Ottawa, ON, Canada
| | - B Wang
- University of Ottawa, Ottawa, ON, Canada
| | - R Bergeron
- University of Ottawa, Ottawa, ON, Canada; Ottawa Hospital Research Institute, Ottawa, ON, Canada.
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Still NAAG’ing After All These Years. NEUROPSYCHOPHARMACOLOGY: A TRIBUTE TO JOSEPH T. COYLE 2016; 76:215-55. [DOI: 10.1016/bs.apha.2016.01.007] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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Khacho P, Wang B, Ahlskog N, Hristova E, Bergeron R. Differential effects of N-acetyl-aspartyl-glutamate on synaptic and extrasynaptic NMDA receptors are subunit- and pH-dependent in the CA1 region of the mouse hippocampus. Neurobiol Dis 2015; 82:580-592. [PMID: 26303888 DOI: 10.1016/j.nbd.2015.08.017] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Revised: 08/13/2015] [Accepted: 08/17/2015] [Indexed: 11/30/2022] Open
Abstract
Ischemic strokes cause excessive release of glutamate, leading to overactivation of N-methyl-d-aspartate receptors (NMDARs) and excitotoxicity-induced neuronal death. For this reason, inhibition of NMDARs has been a central focus in identifying mechanisms to avert this extensive neuronal damage. N-acetyl-aspartyl-glutamate (NAAG), the most abundant neuropeptide in the brain, is neuroprotective in ischemic conditions in vivo. Despite this evidence, the exact mechanism underlying its neuroprotection, and more specifically its effect on NMDARs, is currently unknown due to conflicting results in the literature. Here, we uncover a pH-dependent subunit-specific action of NAAG on NMDARs. Using whole-cell electrophysiological recordings on acute hippocampal slices from adult mice and on HEK293 cells, we found that NAAG increases synaptic GluN2A-containing NMDAR EPSCs, while effectively decreasing extrasynaptic GluN2B-containing NMDAR EPSCs in physiological pH. Intriguingly, the results of our study further show that in low pH, which is a physiological occurrence during ischemia, NAAG depresses GluN2A-containing NMDAR EPSCs and amplifies its inhibitory effect on GluN2B-containing NMDAR EPSCs, as well as upregulates the surface expression of the GluN2A subunit. Altogether, our data demonstrate that NAAG has differential effects on NMDAR function based on subunit composition and pH. These findings suggest that the role of NAAG as a neuroprotective agent during an ischemic stroke is likely mediated by its ability to reduce NMDAR excitation. The inhibitory effect of NAAG on NMDARs and its enhanced function in acidic conditions make NAAG a prime therapeutic agent for the treatment of ischemic events.
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Affiliation(s)
- Pamela Khacho
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Boyang Wang
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Nina Ahlskog
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Elitza Hristova
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
| | - Richard Bergeron
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada; Department of Psychiatry, University of Ottawa, Ottawa, ON K1Z 7K4, Canada; Neuroscience Program, Ottawa Hospital Research Institute, Ottawa, ON K1Y 4E9, Canada.
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N -acetyl-aspartyl-glutamate and inhibition of glutamate carboxypeptidases protects against soman-induced neuropathology. Neurotoxicology 2015; 48:180-91. [DOI: 10.1016/j.neuro.2015.03.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 02/26/2015] [Accepted: 03/13/2015] [Indexed: 12/31/2022]
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O'Neill J, Seese R, Hudkins M, Siddarth P, Levitt J, Tseng PB, Wu KN, Gurbani S, Shields WD, Caplan R. 1H MRSI and social communication deficits in pediatric complex partial seizures. Epilepsia 2011; 52:1705-14. [PMID: 21635240 DOI: 10.1111/j.1528-1167.2011.03114.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
PURPOSE To investigate relationships between regional brain metabolites, social communication deficits, and seizure frequency in children and adolescents with cryptogenic epilepsy with complex partial seizures (CPS). METHODS In 12 children and adolescents with CPS and 23 age- and gender-matched healthy controls, we acquired proton magnetic resonance spectroscopic imaging (MRSI) at 1.5 T and 30 ms echo-time from bilateral inferior frontal and superior temporal gyri, regions associated with social communication deficits. Videotaped speech samples of all the subjects were coded for social communication deficits and parents provided information on seizure frequency. KEY FINDINGS Four MRSI findings emerged in right inferior frontal gyrus. N-acetyl-aspartate (NAA) plus N-acetyl-aspartyl-glutamate (NAAG)--together called "tNAA"--was 11.4% lower in patients with CPS than in controls. Choline-compounds (Cho) were 15.4% lower in CPS than in controls. Within CPS, higher tNAA was associated with more frequent seizures and abnormal social communication. SIGNIFICANCE Localization of findings to right inferior frontal cortex supports the involvement of this area in social communication deficits and may be related to atypical lateralization of expressive language in pediatric epilepsy. Lower levels of tNAA and Cho may indicate local neuronal or glial damage or underpopulation due to excitotoxicity or other causes. The sensitivity of tNAA to seizure frequency suggests effects of ongoing CPS on neuronal and glial function in this brain region.
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Affiliation(s)
- Joseph O'Neill
- Division of Child and Adolescent Psychiatry, UCLA Semel Institute for Neurosciences, Los Angeles, California 90024-1759, USA.
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Ghose S, Chin R, Gallegos A, Roberts R, Coyle J, Tamminga C. Localization of NAAG-related gene expression deficits to the anterior hippocampus in schizophrenia. Schizophr Res 2009; 111:131-7. [PMID: 19403271 PMCID: PMC2685203 DOI: 10.1016/j.schres.2009.03.038] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Revised: 03/27/2009] [Accepted: 03/30/2009] [Indexed: 10/20/2022]
Abstract
N-acetyl aspartyl glutamate (NAAG) is an endogenous agonist at the metabotropic glutamate receptor 3 (mGluR3,GRM3) receptor and antagonist at the N-methyl d-aspartate (NMDA) receptor, both receptors important to the pathophysiology of schizophrenia. Glutamate carboxypeptidase II (GCPII), an enzyme that metabolizes NAAG, is also implicated in this illness. In this study, we conducted in situ hybridization experiments to examine expression of mGluR3 and GCPII transcripts along the rostrocaudal axis of the human postmortem hippocampus. We hypothesized that we would find changes in mGluR3 and/or GCPII in the AH but not posterior hippocampus (PH) in schizophrenia. We compared mRNA levels of these genes in the dentate gyrus (DG) and cornu ammonis (CA)1 and CA3 of AH and PH in 20 matched pairs of control and schizophrenia cases. In controls, mGluR3 is highly expressed in the DG and at lower levels in CA1 and CA3 while GCP II is expressed at similar levels in these regions. Group comparisons show a significant reduction of GCPII mRNA level in the AH in schizophrenia. Post hoc analyses reveal this difference is localized to the CA1 region. In addition, we find a significant positive correlation between GCPII and mGluR3 mRNA in the CA3 of the control AH (r=0.66, p=0.008) which is not present in schizophrenia (r=0.096, p=0.76). This may reflect a disrupted functional interaction between NAAG and mGluR3 in CA3 in schizophrenia. These data suggest that NAAG-mediated signaling is disrupted in the AH in schizophrenia and localize the defect to the CA1 and CA3 regions.
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Affiliation(s)
- Subroto Ghose
- University of Texas Southwestern Medical Center, Dallas, TX 75390-9127, USA.
| | - Ronald Chin
- 5323 Harry Hines Boulevard, NE5. 110, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Analysa Gallegos
- 5323 Harry Hines Boulevard, NE5. 110, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Rosalinda Roberts
- Maryland Psychiatric Research Center, 55 Wade Avenue, Catonsville, MD, USA
| | - Joseph Coyle
- 115 Mill Street, Belmont, MA Mclean Hospital, Harvard Medical School, MA, USA
| | - Carol Tamminga
- 5323 Harry Hines Boulevard, NE5. 110, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Zhao J, Ramadan E, Cappiello M, Wroblewska B, Bzdega T, Neale JH. NAAG inhibits KCl-induced [3H]-GABA release via mGluR3, cAMP, PKA and L-type calcium conductance. Eur J Neurosci 2008. [DOI: 10.1111/j.1460-9568.2001.01396.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Han L, Wong DL, Tsai G, Jiang Z, Coyle JT. Promoter analysis of human glutamate carboxypeptidase II. Brain Res 2007; 1170:1-12. [PMID: 17689503 PMCID: PMC2706136 DOI: 10.1016/j.brainres.2007.07.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 07/04/2007] [Accepted: 07/10/2007] [Indexed: 10/23/2022]
Abstract
The expression of glutamate carboxypeptidase II (GCP II) is reduced in selective brain regions in schizophrenic patients. To investigate transcriptional mechanisms regulating the human GCP II gene, a 3460 bp DNA fragment comprised of the proximal 3228 bp of 5' untranscribed sequence and first 232 bp of 5' UTR portion of this gene was cloned into the mammalian luciferase reporter gene vector pGL3-Basic. Transfection assays in human astrocyte-derived SVG and human prostate tumor-derived LNCaP cells demonstrated that constructs with 3460, 1590 and 761 bp portions of 5' region of human GCP II gene were able to drive the luciferase reporter gene. Additional deletion constructs showed that in the SVG cell line, constructs with 511 and 411 bp of GCP II gene fragments yielded highest transcriptional activity, with declining activity upon further removal of 5' sequences. 15 bp of the promoter 5' to a 225 bp GCP II fragment were essential for luciferase expression. Thus, in the SVG cells, the proximal 240 bp of the human GCP II promoter (232 bp of the 5' UTR and 8 bp of 5' untranscribed sequences) may represent the core promoter. Further, while a LyF-1 site lies within and overlaps a transcription start site in the 15 bp sequence, site-directed mutagenesis shows that LyF-1 is not the transcription initiator for the "TATA and CAAT" box lacking GCP II gene in the SVG cells. Finally, pattern differences in GCP II gene promoter expression in SVG and LNCaP cells suggest that sequences beyond 240 bp may be important for tissue-specific GCP II expression.
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Affiliation(s)
- Liqun Han
- Laboratory of Molecular and Psychiatric Neuroscience, Department of Psychiatry, Harvard Medical School and McLean Hospital, Belmont, MA 02478, USA
| | - Dona Lee Wong
- Laboratory of Molecular and Developmental Neurobiology, Department of Psychiatry, Harvard Medical School and McLean Hospital, Belmont, MA 02478, USA
| | - Guochuan Tsai
- Department of Psychiatry, Harbor-UCLA Medical Center, Torrance, CA 90509, USA
| | - Zhichun Jiang
- Department of Psychiatry, Harbor-UCLA Medical Center, Torrance, CA 90509, USA
| | - Joseph T. Coyle
- Laboratory of Molecular and Psychiatric Neuroscience, Department of Psychiatry, Harvard Medical School and McLean Hospital, Belmont, MA 02478, USA
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Mateo Z, Porter JT. Group II metabotropic glutamate receptors inhibit glutamate release at thalamocortical synapses in the developing somatosensory cortex. Neuroscience 2007; 146:1062-72. [PMID: 17418955 PMCID: PMC3690373 DOI: 10.1016/j.neuroscience.2007.02.053] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2006] [Revised: 02/15/2007] [Accepted: 02/21/2007] [Indexed: 11/26/2022]
Abstract
Thalamocortical synapses provide a strong glutamatergic excitation to cortical neurons that is critical for processing sensory information. Unit recordings in vivo indicate that metabotropic glutamate receptors (mGluRs) reduce the effect of thalamocortical input on cortical circuits. However, it is not known whether this reduction is due to a reduction in glutamate release from thalamocortical terminals or from a decrease in cortical neuron excitability. To directly determine whether mGluRs act as autoreceptors on thalamocortical terminals, we examined the effect of mGluR agonists on thalamocortical synapses in slices. Thalamocortical excitatory postsynaptic currents (EPSCs) were recorded in layer IV cortical neurons in developing mouse brain slices. The activation of group II mGluRs with (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG IV) reduced thalamocortical EPSCs in both excitatory and inhibitory neurons, while the stimulation of group I or group III mGluRs had no effect on thalamocortical EPSCs. Consistent with a reduction in glutamate release, DCG IV increased the paired pulse ratio and the coefficient of variation of the EPSCs. The reduction induced by DCG IV was reversed by the group II mGluR antagonist, LY341495, and mimicked by another selective group II agonist, (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylic acid (APDC). The mGluR2 subtype appears to mediate the reduction of thalamocortical EPSCs, since the selective mGluR3 agonist, N-acetylaspartylglutamate (NAAG), had no effect on the EPSCs. Consistent with this, we showed that mGluR2 is expressed in the barrels. Furthermore, blocking group II mGluRs with LY341495 reduced the synaptic depression induced by a short stimulus train, indicating that synaptically released glutamate activates these receptors. These results indicate that group II mGluRs modulate thalamocortical processing by inhibiting glutamate release from thalamocortical synapses. This inhibition provides a feedback mechanism for preventing excessive excitation of cortical neurons that could play a role in the plasticity and refinement of thalamocortical connections during this early developmental period.
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Affiliation(s)
- Z Mateo
- Department of Physiology, Pharmacology and Toxicology, Ponce School of Medicine, PO Box 7004, Ponce, Puerto Rico 00732
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Bergeron R, Imamura Y, Frangioni JV, Greene RW, Coyle JT. Endogenous N-acetylaspartylglutamate reduced NMDA receptor-dependent current neurotransmission in the CA1 area of the hippocampus. J Neurochem 2007; 100:346-57. [PMID: 17241157 DOI: 10.1111/j.1471-4159.2006.04253.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
N-Acetylaspartylglutamate (NAAG) is a neuropeptide found in high concentrations in the brain. Using whole-cell recordings of CA1 pyramidal neurons in acute hippocampal slices, we found that either (i) the application of exogenous NAAG or (ii) an increase of endogenous extracellular NAAG, caused by the inhibition of its catabolic enzyme glutamate carboxypeptidase II (GCP II), resulted in a significant reduction in the amplitude of the isolated NMDA receptor (NMDAR) component of the evoked excitatory postsynaptic current (EPSC). Conversely, reduction of endogenous extracellular NAAG caused by either (i) perfusion with a soluble form of pure human GCP II or (ii) affinity purified antibodies against NAAG, enhanced the amplitude of the isolated NMDAR current. Bath application of GCP II inhibitor induced a progressive loss of spontaneous NMDAR miniatures. Furthermore, NAAG blocked the induction of long-term potentiation at Schaffer collateral axons-CA1 pyramidal neuron synapses. All together, these results suggest that NAAG acts as an endogenous modulator of NMDARs in the CA1 area of the hippocampus.
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Affiliation(s)
- Richard Bergeron
- Ottawa Health Research Institute, Department of Psychiatry, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada.
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Meyerhoff JL, Yourick DL, Slusher BS, Long JB. N-acetylaspartylglutamate (NAAG) in spinal cord injury and disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2006; 576:339-51; discussion 361-3. [PMID: 16802725 DOI: 10.1007/0-387-30172-0_25] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Affiliation(s)
- James L Meyerhoff
- Division of Neuroscience, Walter Reed Army Institute of Research, 503 Robert Grant Ave., Silver Spring, MD 20910-7500, USA.
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Mesters JR, Barinka C, Li W, Tsukamoto T, Majer P, Slusher BS, Konvalinka J, Hilgenfeld R. Structure of glutamate carboxypeptidase II, a drug target in neuronal damage and prostate cancer. EMBO J 2006; 25:1375-84. [PMID: 16467855 PMCID: PMC1422165 DOI: 10.1038/sj.emboj.7600969] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2005] [Accepted: 12/23/2005] [Indexed: 11/09/2022] Open
Abstract
Membrane-bound glutamate carboxypeptidase II (GCPII) is a zinc metalloenzyme that catalyzes the hydrolysis of the neurotransmitter N-acetyl-L-aspartyl-L-glutamate (NAAG) to N-acetyl-L-aspartate and L-glutamate (which is itself a neurotransmitter). Potent and selective GCPII inhibitors have been shown to decrease brain glutamate and provide neuroprotection in preclinical models of stroke, amyotrophic lateral sclerosis, and neuropathic pain. Here, we report crystal structures of the extracellular part of GCPII in complex with both potent and weak inhibitors and with glutamate, the product of the enzyme's hydrolysis reaction, at 2.0, 2.4, and 2.2 A resolution, respectively. GCPII folds into three domains: protease-like, apical, and C-terminal. All three participate in substrate binding, with two of them directly involved in C-terminal glutamate recognition. One of the carbohydrate moieties of the enzyme is essential for homodimer formation of GCPII. The three-dimensional structures presented here reveal an induced-fit substrate-binding mode of this key enzyme and provide essential information for the design of GCPII inhibitors useful in the treatment of neuronal diseases and prostate cancer.
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Affiliation(s)
- Jeroen R Mesters
- Institute of Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, Lübeck, Germany
| | - Cyril Barinka
- Institute of Organic Chemistry and Biochemistry, Academy of Science of the Czech Republic, Prague, Czech Republic
| | - Weixing Li
- Guilford Pharmaceuticals Inc., Baltimore, MD, USA
| | | | - Pavel Majer
- Guilford Pharmaceuticals Inc., Baltimore, MD, USA
| | | | - Jan Konvalinka
- Institute of Organic Chemistry and Biochemistry, Academy of Science of the Czech Republic, Prague, Czech Republic
| | - Rolf Hilgenfeld
- Institute of Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, Lübeck, Germany
- Institute of Biochemistry, Center for Structural and Cell Biology in Medicine (CSCM), University of Lübeck, Ratzeburger Allee 160, D-23538 Lübeck, Germany. Tel.: +49 451 500 4060; Fax: +49 451 500 4068; E-mail:
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Long JB, Yourick DL, Slusher BS, Robinson MB, Meyerhoff JL. Inhibition of glutamate carboxypeptidase II (NAALADase) protects against dynorphin A-induced ischemic spinal cord injury in rats. Eur J Pharmacol 2005; 508:115-22. [PMID: 15680261 DOI: 10.1016/j.ejphar.2004.12.008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Revised: 12/01/2004] [Accepted: 12/06/2004] [Indexed: 11/27/2022]
Abstract
Glutamate carboxypeptidase (GCP) II (EC 3.4.17.21), which is also known as N-acetylated-alpha-linked acidic dipeptidase (NAALADase), hydrolyses the endogenous acidic dipeptide N-acetylaspartylglutamate (NAAG), yielding N-acetyl-aspartate and glutamate. Inhibition of this enzyme by 2-(phosphonomethyl) pentanedioic acid (2-PMPA) has been shown to protect against ischemic injury to the brain and hypoxic and metabolic injury to neuronal cells in culture, presumably by increasing and decreasing the extracellular concentrations of NAAG and glutamate, respectively. Since both NAAG and GCP II are found in especially high concentrations in the spinal cord, injuries to the spinal cord involving pathophysiological elevations in extracellular glutamate might be particularly responsive to GCP II inhibition. Lumbar subarachnoid injections of dynorphin A in rats cause ischemic spinal cord injury, elevated extracellular glutamate and a persistent hindlimb paralysis that is mediated through excitatory amino acid receptors. We therefore used this injury model to evaluate the protective effects of 2-PMPA. When coadministered with dynorphin A, 2-PMPA significantly attenuated the dynorphin A-induced elevations in cerebrospinal fluid glutamate levels and by 24 h postinjection caused significant dose-dependent improvements in motor scores that were associated with marked histopathological improvements. These results indicate that 2-PMPA provides effective protection against excitotoxic spinal cord injury.
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Affiliation(s)
- Joseph B Long
- Department of Polytrauma and Resuscitation Research, Division of Military Casualty Research, Walter Reed Army Institute of Research, Silver Spring, MD 20910-7500, USA.
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16
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Bergeron R, Coyle JT, Tsai G, Greene RW. NAAG reduces NMDA receptor current in CA1 hippocampal pyramidal neurons of acute slices and dissociated neurons. Neuropsychopharmacology 2005; 30:7-16. [PMID: 15354184 DOI: 10.1038/sj.npp.1300559] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
N-acetylaspartylglutamate (NAAG) is an abundant neuropeptide in the nervous system, yet its functions are not well understood. Pyramidal neurons of the CA1 sector of acutely prepared hippocampal slices were recorded using the whole-cell patch-clamp technique. At low concentrations (20 microM), NAAG reduced isolated N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic currents or NMDA-induced currents. The NAAG-induced change in the NMDA concentration/response curve suggested that the antagonism was not competitive. However, the NAAG-induced change in the concentration/response curve for the NMDAR co-agonist, glycine, indicated that glycine can overcome the NAAG antagonism. The antagonism of the NMDAR induced by NAAG was still observed in the presence of LY-341495, a potent and selective mGluR3 antagonist. Moreover, in dissociated pyramidal neurons of the CA1 region, NAAG also reduced the NMDA current and this effect was reversed by glycine. These results suggest that NAAG reduces the NMDA currents in hippocampal CA1 pyramidal neurons.
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Turner JP, Salt TE. Group II and III metabotropic glutamate receptors and the control of the nucleus reticularis thalami input to rat thalamocortical neurones in vitro. Neuroscience 2004; 122:459-69. [PMID: 14614910 DOI: 10.1016/j.neuroscience.2003.08.014] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Intracellular recordings were made from neurones in the thalamic reticular nucleus (TRN) and ventro-basal (VB) thalamus in slices of rat midbrain in vitro. Electrical stimulation of the medial lemniscus or TRN resulted in the generation of complex synaptic potentials containing disynaptic inhibitory post-synaptic potentials (IPSPs) in VB thalamocortical neurones. Analysis of the excitatory synaptic responses in TRN neurones indicates they can produce burst output response irrespective of the level of sub-threshold membrane potential. This suggests that network-evoked IPSPs in VB thalamocortical neurones occur following a burst of TRN action potentials. Using ionotropic glutamate receptor antagonists, the activation of these disynaptic events was blocked, and the monosynaptic IPSPs that resulted from the direct activation of the TRN could be isolated. The selective Group II agonists LY354740 (1-10 microM) and N-acetyl-aspartyl-glutamate (NAAG; 100-500 microM) both caused a reversible depression of these monosynaptic TRN IPSPs without any effect on membrane potential or input resistance. Likewise, the specific Group III agonist L-2-amino-4-phosphonobutanoate (10-500 microM), but not (RS)-4-phosphonophenylglycine (1 and 30 microM) also caused a reversible depression of these IPSPs, again without any effect on membrane potential or input resistance.Thus, the IPSPs recorded in VB thalamocortical neurones, evoked by TRN activation, can be depressed by the activation of either Group II or III metabotropic glutamate receptors. This is consistent with the location of these receptor types on the presynaptic terminals of TRN axons in the VB thalamus. This raises the possibility that, during periods of intense excitatory activity, glutamate release could influence the release of GABA from TRN axon terminals in the thalamus. In addition, as NAAG is located in the axons and terminals arising from the TRN, there is the possibility that this dipeptide is also released by these terminals to control the release of GABA during periods of high activity in the TRN.
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Affiliation(s)
- J P Turner
- Department of Visual Science, Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK.
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Sanabria ERG, Wozniak KM, Slusher BS, Keller A. GCP II (NAALADase) inhibition suppresses mossy fiber-CA3 synaptic neurotransmission by a presynaptic mechanism. J Neurophysiol 2004; 91:182-93. [PMID: 12917384 PMCID: PMC2810521 DOI: 10.1152/jn.00465.2003] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We tested the hypothesis that endogenous N-acetylaspartylglutamate (NAAG) presynaptically inhibits glutamate release at mossy fiber-CA3 synapses. For this purpose, we made use of 2-(3-mercaptopropyl)pentanedioic acid (2-MPPA), an inhibitor of glutamate carboxypeptidase II [GCP II; also known as N-acetylated alpha-linked acidic dipeptidase (NAALADase)], the enzyme that hydrolyzes NAAG into N-acetylaspartate and glutamate. Application of 2-MPPA (1-20 microM) had no effect on intrinsic membrane properties of CA3 pyramidal neurons recorded in vitro in whole cell current- or voltage-clamp mode. Bath application of 10 microM 2-MPPA suppressed evoked excitatory postsynaptic current (EPSC) amplitudes. Attenuation of EPSC amplitudes was accompanied by a significant increase in paired-pulse facilitation (50-ms interpulse intervals), suggesting that a presynaptic mechanism is involved. The group II metabotropic glutamate receptor (mGluR) antagonist 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-y l) propanoic acid (LY341495) prevented the 2-MPPA-dependent suppression of EPSC amplitudes. 2-MPPA reduced the frequencies of TTX-insensitive miniature EPSCs (mEPSC), without affecting their amplitudes, further supporting a presynaptic action for GCP II inhibition. 2-MPPA-induced reduction of mEPSC frequencies was prevented by LY341495, reinforcing the role of presynaptic group II mGluR. Because GCP II inhibition is thought to increase NAAG levels, these results suggest that NAAG suppresses synaptic transmission at mossy fiber-CA3 synapses through presynaptic activation of group II mGluRs.
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Affiliation(s)
- Emilio R Garrido Sanabria
- Department of Anatomy and Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore 21201, USA
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19
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Yourick DL, Koenig ML, Durden AV, Long JB. N-acetylaspartylglutamate and β-NAAG protect against injury induced by NMDA and hypoxia in primary spinal cord cultures. Brain Res 2003; 991:56-64. [PMID: 14575876 DOI: 10.1016/s0006-8993(03)03533-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The acidic dipeptide N-acetylaspartylglutamate (NAAG) is the most prevalent peptide in the central nervous system. NAAG is a low potency agonist at the NMDA receptor, and hydrolysis of NAAG yields the more potent excitatory amino acid neurotransmitter glutamate. beta-NAAG is a competitive inhibitor of the NAAG hydrolyzing enzyme N-acetylated alpha-linked acidic dipeptidase (NAAG peptidase activity) or glutamate carboxypeptidase II, and may also act as a NAAG-mimetic at some of the sites of NAAG pharmacological activity. Since NAAG has been shown to have neuroprotective characteristics in a number of experimental preparations, it is the purpose of the present study to specifically evaluate the possible efficacy of NAAG and beta-NAAG against NMDA- and hypoxia-induced injury to spinal cord mixed neuronal and glial cell cultures. NAAG (500-1000 microM) protected against NMDA- or hypoxia-induced injuries to spinal cord cultures, and the nonhydrolyzable analog beta-NAAG (250-1000 microM) completely eliminated the loss of viability caused by either insult. Both peptides also attenuated NMDA-induced increases in intraneuronal Ca(2+). Nonspecific mGluR antagonists, pertussis toxin, a stable cAMP analog, and manipulation of NAAG peptidase activity did not by themselves alter cell damage and did not influence the neuroprotective effects of NAAG. NAAG was not protective against kainate- or AMPA-induced cellular injury, while beta-NAAG was partially neuroprotective against both insults. At 2 mM, NAAG and beta-NAAG reduced neuronal survival and increased intraneuronal Ca(2+); these effects were only marginally attenuated by dizocilpine and APV. The results indicate that NAAG and beta-NAAG protect against excitotoxic and hypoxic injury to spinal cord neurons, and do so predominantly by interactions with NMDA and not mGluR receptors.
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Affiliation(s)
- Debra L Yourick
- Division of Neurosciences, Walter Reed Army Institute of Research, 503 Robert Grant Ave, Silver Spring, MD 20910-7500, USA.
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20
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Tsai G, Dunham KS, Drager U, Grier A, Anderson C, Collura J, Coyle JT. Early embryonic death of glutamate carboxypeptidase II (NAALADase) homozygous mutants. Synapse 2003; 50:285-92. [PMID: 14556233 DOI: 10.1002/syn.10263] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Glutamate carboxypeptidase II (EC 3.4.17.21) catalyzes the hydrolysis (Km = 0.2 microM) of the neuropeptide N-acetylaspartylglutamate to yield N-acetylaspartate and glutamate and also serves as a high-affinity folate hydrolase in the gut, cleaving the polyglutamate chain to permit the absorption of folate. N-acetylaspartylglutamate is an agonist at the mGluR3 metabotropic receptor and a source of extracellular glutamate through hydrolysis by glutamate carboxypeptidase II. Given the important role of glutamate in brain development and function, we were interested in the effects of a null mutation of glutamate carboxypeptidase II that would potentiate the effects of N-acetylaspartylglutamate. The PGK-Neomycin cassette was inserted to delete exons 9 and 10, which we previously demonstrated encode for the zinc ligand domain essential for enzyme activity. Successful germline transmission was obtained from chimeras derived from embryonic stem cells with the targeted mutation of glutamate carboxypeptidase II. Homozygous null mutants did not survive beyond embryonic day 8. Folate supplementation of the heterozygous mothers did not rescue the homozygous embryos. Mice heterozygous for the null mutation appeared grossly normal and expressed both mutated and wild-type mRNA but the activity of glutamate carboxypeptidase II is comparable to the wild-type mice. The results indicate that the expression of glutamate carboxypeptidase II is upregulated when one allele is inactivated and that its activity is essential for early embryogenesis.
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Affiliation(s)
- G Tsai
- Laboratory of Molecular and Psychiatric Neuroscience, Mailman Research Center, McLean Hospital Department of Psychiatry, Harvard Medical School, Cambridge, Massachusetts, USA
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21
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Carpenter KJ, Sen S, Matthews EA, Flatters SL, Wozniak KM, Slusher BS, Dickenson AH. Effects of GCP-II inhibition on responses of dorsal horn neurones after inflammation and neuropathy: an electrophysiological study in the rat. Neuropeptides 2003; 37:298-306. [PMID: 14607107 DOI: 10.1016/j.npep.2003.08.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
N-Acetylaspartylglutamate (NAAG) is a peptide neurotransmitter present in the brain and spinal cord. It is hydrolysed by glutamate carboxypeptidase II (GCPII); thus, the GCP-II inhibitor 2-[phosphono-methyl]-pentanedioic acid (2-PMPA) protects endogenous NAAG from degradation, allowing its effects to be studied in vivo. We recorded the effect of spinal 2-PMPA (50-1000 microg) on the electrical-evoked activity of dorsal horn neurones in normal and carrageenan-inflamed animals, and in the spinal nerve ligation (SNL) model of neuropathy and sham-operated animals. In normal animals, 1000 microg 2-PMPA selectively inhibited noxious-evoked activity (input, post-discharge and C- and Adelta-fibre-evoked responses), and not low threshold Abeta-fibre-evoked responses. After carrageenan inflammation, the lower dose of 100 microg 2-PMPA inhibited input, post-discharge, C- and Adelta-fibre-evoked responses by a significantly greater amount than the same dose in normal animals. 2-PMPA inhibited neuronal responses less consistently in sham-operated and SNL animals, and effects were not significantly different from those seen in normal animals. NAAG is an agonist at the inhibitory metabotropic glutamate receptor mGluR3, and 2-PMPA may inhibit nociceptive transmission in normal animals by elevating synaptic NAAG levels, allowing it to activate mGluR3 and thus reducing transmitter release from afferent nerve terminals. mGluR3 expression in the superficial dorsal horn is upregulated after peripheral inflammation, perhaps explaining the greater inhibition of neuronal responses we observed after carrageenan inflammation. These results support an important role of endogenous NAAG in the spinal processing of noxious information.
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Affiliation(s)
- Katherine J Carpenter
- Department of Pharmacology, University College London, Gower Street, London,WC1E 6BT, UK
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22
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Flores C, Coyle JT. Regulation of glutamate carboxypeptidase II function in corticolimbic regions of rat brain by phencyclidine, haloperidol, and clozapine. Neuropsychopharmacology 2003; 28:1227-34. [PMID: 12700705 DOI: 10.1038/sj.npp.1300129] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Mounting evidence indicates that hypofunction of NMDA glutamate receptors causes or contributes to the full symptomatology of schizophrenia. N-acetyl-aspartyl-glutamate (NAAG), an endogenous neuropeptide, blocks NMDA receptors and inhibits glutamate release by activating metabotropic mGluR3 receptors. NAAG is catabolized to glutamate and N-acetyl-aspartate by the astrocytic enzyme glutamate carboxypeptidase II (GCP II). Changes in GCP II activity may be critically linked to changes in glutamatergic neurotransmission especially at NMDA receptors. We examined whether GCP II function is altered by treatment with the noncompetitive antagonist and psychotomimetic drug phencyclidine (PCP) and with the neuroleptics haloperidol (HAL) and clozapine (CLOZ), in corticolimbic brain regions of the adult rat. Chronic exposure to PCP produced significant increases in GCP II protein expression and activity in the prefrontal cortex (PFC) and hippocampus (HIPP). This effect may be explained by a compensatory response to persistent blockade of NMDA receptors. In addition, chronic treatment with neuroleptics upregulated GCP II activity, but not protein expression, in the PFC. In contrast, GCP II activity was decreased after acute exposure to HAL or CLOZ and was not changed after acute PCP treatment. These findings provide support for a role of GCP II function in the control of glutamatergic neurotransmission and suggest that some of the therapeutic actions of neuroleptic drugs may be mediated through their effects on GCP II activity. These results demonstrate that psychotomimetic and neuroleptic drugs modulate GCP II function in brain regions that are widely involved in the neuropathology of schizophrenia.
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Affiliation(s)
- Cecilia Flores
- Department of Psychiatry, Harvard Medical School and McLean Hospital, Mailman Research Center, Belmont, MA, USA.
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23
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Witkin JM, Gasior M, Schad C, Zapata A, Shippenberg T, Hartman T, Slusher BS. NAALADase (GCP II) inhibition prevents cocaine-kindled seizures. Neuropharmacology 2002; 43:348-56. [PMID: 12243764 DOI: 10.1016/s0028-3908(02)00124-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The prediction that inhibition of NAALADase, an enzyme catalyzing the cleavage of glutamate from N-acetyl-aspartyl-glutamate, would produce antiepileptogenic effects against cocaine was tested. Cocaine kindled seizures were developed in male, Swiss-Webster mice by daily administration of 60 mg/kg cocaine for 5 days. The NAALADase inhibitor 2-(phosphonomethyl)pentanedioic acid (2-PMPA) produced dose-dependent protection (10-100 mg/kg) against both the development of seizure kindling and the occurrence of seizures during the kindling process without observable behavioral side-effects. It is not likely that 2-PMPA produced protection against cocaine kindling by altering the potency of the convulsant stimulus as daily administration of 2-PMPA did not alter the convulsant thresholds for cocaine. Lower daily doses of cocaine (40 mg/kg) did not increase the incidence of seizures but produced kindling, as evidenced by the increase in seizure susceptibility when mice were probed with a higher dose of cocaine. 2-PMPA was also effective in preventing the development of sensitization to this covert kindling process. In contrast to its efficacy against cocaine kindled seizures, 2-PMPA failed to attenuate the convulsions engendered by acute challenges with pentylenetetrazole, bicuculline, N-methyl-D-aspartate, maximal electroshock or cocaine. Similarly, acutely-administered 2-PMPA did not block cocaine seizures in fully-kindled mice. NAALADase inhibition thus provides a novel means of attenuating the development of cocaine seizure kindling.
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Affiliation(s)
- Jeffrey M Witkin
- Drug Development Group, Addiction Research Center, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA.
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24
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Greene R. Circuit analysis of NMDAR hypofunction in the hippocampus, in vitro, and psychosis of schizophrenia. Hippocampus 2002; 11:569-77. [PMID: 11732709 DOI: 10.1002/hipo.1072] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
NMDA antagonists provide the best pharmacological model of psychosis-related schizophrenia. Data from circuit analysis of the effects of the antagonism of NMDA receptors in the CA1 region of the hippocampus of rats in vitro suggest a hypothesis concerning cortical circuit dysfunction responsible for NMDA antagonist-dependent psychosis, relevant to the psychosis associated with schizophrenia. The NMDA antagonists may act by causing a selective, partial, disinhibition of cortical projection cells. The effects are partially due to the partial role of NMDA-dependent transmission in the excitatory glutamate drive of interneurons. Characterization of the selectivity is incomplete, but includes disinhibition of the recurrent inhibitory circuit and is concentration-sensitive. It may result from differences in NMDA receptors (NMDARs) on interneurons. At higher concentrations, antagonism of all NMDA-dependent transmission results in anesthesia. At low concentration, selective blockade of NMDA-dependent LTP of the recurrent inhibitory circuit may disrupt particular aspects of information processing involving learning and/or memory, consistent with the generation of abnormal associations. An endogenous peptide, NAAG, is shown to antagonize NMDARs in a manner similar to known psychotogenic agents like ketamine or phencyclidine. Finally, mechanisms that could enhance NMDAR function are discussed as possible therapeutic strategies for psychosis.
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Affiliation(s)
- R Greene
- Department of Psychiatry, Harvard Medical School and VAMC, Brockton, Massachusetts, USA.
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25
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Gafurov B, Urazaev AK, Grossfeld RM, Lieberman EM. N-acetylaspartylglutamate (NAAG) is the probable mediator of axon-to-glia signaling in the crayfish medial giant nerve fiber. Neuroscience 2002; 106:227-35. [PMID: 11564432 DOI: 10.1016/s0306-4522(01)00271-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Glial cell hyperpolarization previously has been reported to be induced by high frequency stimulation or glutamate. We now report that it also is produced by the glutamate-containing dipeptide N-acetylaspartylglutamate (NAAG), by its non-hydrolyzable analog beta-NAAG, and by NAAG in the presence of 2-(phosphonomethyl)-pentanedioic acid (2-PMPA), a potent inhibitor of the NAAG degradative enzyme glutamate carboxypeptidase II. The results indicate that NAAG mimics the effect of nerve fiber stimulation on the glia. Although glutamate has a similar effect, the other presumed product of NAAG hydrolysis, N-acetylaspartate, is without effect on glial cell membrane potential, as is aspartylglutamate (in the presence of 2-PMPA). The hyperpolarization induced by stimulation, glutamate, NAAG, beta-NAAG, or NAAG plus 2-PMPA is completely blocked by the Group II metabotropic glutamate receptor antagonist (S)-alpha-ethylglutamate but is not altered by antagonists of Group I or III metabotropic glutamate receptors. The N-methyl-D-aspartate receptor antagonist MK801 reduces but does not eliminate the hyperpolarization generated by glutamate, NAAG or stimulation. These results, in combination with those of the preceding paper, are consistent with the premise that NAAG could be the primary axon-to-glia signaling agent. When the unstimulated nerve fiber is treated with cysteate, a glutamate reuptake blocker, there is a small hyperpolarization of the glial cell that can be substantially reduced by pretreatment with 2-PMPA before addition of cysteate. A similar effect of cysteate is seen during a 50 Hz/5 s stimulation. From these results we suggest that glutamate derived from NAAG hydrolysis appears in the periaxonal space under the conditions of these experiments and may contribute to the glial hyperpolarization.
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Affiliation(s)
- B Gafurov
- Department of Physiology, The Brody School of Medicine of East Carolina University, Greenville, NC 27858, USA
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26
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Sekiguchi M, Wada K, Wenthold RJ. N
-Acetylaspartylglutamate acts as an agonist upon homomeric NMDA receptor (NMDAR1) expressed in Xenopus
oocytes. FEBS Lett 2001; 311:285-9. [PMID: 1356833 DOI: 10.1016/0014-5793(92)81121-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The electrophysiological effects of N-acetylaspartylglutamate (NAAG), an endogenous peptide restrictively distributed in the central nervous system, were studied using Xenopus oocytes injected with RNAs transcribed from cloned glutamate receptor cDNAs. NAAG induced an inward current, dose dependently, in oocytes injected with RNA for an N-methyl-D-aspartate receptor subunit (NMDAR1). In contrast, the oocytes injected with RNAs for AMPA-selective glutamate receptors (GluR1, GluR3, GluR1+GluR2 and GluR2+GluR3) scarcely responded to NAAG, and the oocytes injected with RNA for kainate receptor (GluR6) did not respond to NAAG. The half-maximal response (ED50) value of NAAG on expressed NMDAR1 was 185 microM, which shows that NAAG is about 115-times less potent than L-glutamate (Glu), the ED50 of which value was 1.6 microM. The maximal current amplitude induced by NAAG was about 70% of that by Glu. NAAG-induced current in NMDAR1-injected oocytes was potentiated by glycine, dose-dependently antagonized by DL-2-amino-5-phosphonovaleric acid, and blocked by magnesium ions in a voltage-dependent fashion. These results suggest that NAAG is one of the endogenous agonists selective for NMDAR1.
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Affiliation(s)
- M Sekiguchi
- Laboratory of Neurochemistry, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892
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27
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Thomas AG, Liu W, Olkowski JL, Tang Z, Lin Q, Lu XC, Slusher BS. Neuroprotection mediated by glutamate carboxypeptidase II (NAALADase) inhibition requires TGF-beta. Eur J Pharmacol 2001; 430:33-40. [PMID: 11698060 DOI: 10.1016/s0014-2999(01)01239-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Inhibition of glutamate carboxypeptidase (GCP) II (EC 3.4.17.21), also termed N-acetylated alpha-linked acidic dipeptidase (NAALADase), has been shown to protect against ischemic injury presumably via decreasing glutamate and increasing N-acetyl-aspartyl-glutamate (NAAG). NAAG is a potent and selective mGlu3 receptor agonist. Activation of glial mGlu3 receptors has been shown to protect against NMDA toxicity by releasing transforming growth factors, TGF-betas. We hypothesized that GCP II inhibition could be neuroprotective also via TGF-betas, due to increased NAAG. To verify this, Enzyme-Linked Immunosorbent Assays (ELISAs) were performed on media from both control and ischemic cultures treated with the GCP II inhibitor, 2-(phosphonomethyl)-pentanedioic acid (2-PMPA). We found that 2-PMPA attenuated ischemia-induced declines in TGF-beta. To further assess the role of TGF-betas in 2-PMPA-mediated neuroprotection, a neutralizing antibody to TGF-beta (TGF-beta Ab) was used. In both in vitro and in vivo models of cerebral ischemia, TGF-beta Ab reversed the neuroprotection by 2-PMPA. Antibodies to other growth factors had no effect. Data suggests that neuroprotection by GCP II inhibition may be partially mediated by promoting TGF-beta release.
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Affiliation(s)
- A G Thomas
- Guilford Pharmaceuticals Inc., 6611 Tributary Street, Baltimore, MD 21224, USA
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28
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Yamamoto T, Nozaki-Taguchi N, Sakashita Y. Spinal N-acetyl-alpha-linked acidic dipeptidase (NAALADase) inhibition attenuates mechanical allodynia induced by paw carrageenan injection in the rat. Brain Res 2001; 909:138-44. [PMID: 11478930 DOI: 10.1016/s0006-8993(01)02650-6] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
N-Acetylated-alpha-linked acidic dipeptidase (NAALADase) hydrolyzes N-acetyl-aspartyl-glutamate (NAAG) to liberate N-acetyl-aspartate and glutamate. NAAG is a putative neurotransmitter and acts as a mixed agonist/antagonist on N-methyl-D-aspartate (NMDA) receptors and acts as an agonist on the metabotropic glutamate receptor 3 (mGluR3). In the present study, we examined the role of spinal NAALADase in the maintenance of mechanical allodynia induced by carrageenan injection, skin incision and mild thermal injury using 2-(phosphonomethyl)pentanedioic acid (2-PMPA), a specific NAALADase inhibitor, in rats. Mechanical allodynia was induced by injection of 2 mg carrageenan into the paw (carrageenan model), by creating a 1-cm longitudinal skin incision of the plantar aspect of the foot (post-operative model), or by application of thermal stimulation (52.5 degrees C) for 45 s to the hind paw (mild thermal injury model). 2-PMPA was administered intrathecally at the time when the maximum mechanical allodynia occurred. Mechanical allodynia was assessed by the measurement of mechanical threshold using von Frey filaments. The mechanical threshold was measured 5, 15, 30, 60 and 90 min after the drug administration. In the carrageenan model, 100 microg of 2-PMPA attenuated the level of mechanical allodynia. 2-PMPA had no effect on the level of mechanical allodynia in both the post-operative pain model and the mild thermal injury model. These data suggested that the inhibition of spinal NAALADase alleviated mechanical allodynia induced by paw carrageenan injection.
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Affiliation(s)
- T Yamamoto
- Department of Anesthesiology, School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba-shi, 260-0856, Chiba, Japan.
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Yamamoto T, Nozaki-Taguchi N, Sakashita Y, Inagaki T. Inhibition of spinal N-acetylated-alpha-linked acidic dipeptidase produces an antinociceptive effect in the rat formalin test. Neuroscience 2001; 102:473-9. [PMID: 11166133 DOI: 10.1016/s0306-4522(00)00502-9] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
N-acetyl-aspartyl-glutamate is a putative neurotransmitter and acts as a weak agonist at the N-methyl-D-aspartate receptor. N-acetyl-aspartyl-glutamate also acts as an agonist at the metabotropic glutamate receptor 3. N-acetyl-aspartyl-glutamate is hydrolyzed by N-acetylated-alpha-linked acidic dipeptidase to liberate N-acetyl-aspartate and glutamate. Recently, a specific inhibitor of N-acetylated-alpha-linked acidic dipeptidase, 2-(phosphonomethyl)pentanedioic acid, has been reported. In the present study, we examined the effect of i.t. administered 2-(phosphonomethyl)pentanedioic acid in the rat formalin test (a model of inflammatory pain) and the rat hot plate test. In the formalin test, drugs were administered 10min before (pre-treatment study) or 7min after (post-treatment study) the formalin injection. The paw formalin injection induces biphasic flinching (phase 1: 0-2min; phase 2: 10-60min) of the injected paw. In the pre-treatment study, i.t. administered 2-(phosphonomethyl)pentanedioic acid depressed both phases 1 and 2 flinching behavior in a dose-dependent manner but 2-(phosphonomethyl)pentanedioic acid had no effect on the flinching behavior in the post-treatment study. In the pre-treatment study, the potency of 2-(phosphonomethyl)pentanedioic acid in depressing the phase 2 response is greater than that in depressing the phase 1 response. Intrathecal injection of 2-(phosphonomethyl)pentanedioic acid had no effect in the hot plate test. We suggest that N-acetylated-alpha-linked acidic dipeptidase plays an important role in spinal nociceptive transmission and that inhibition of spinal N-acetylated-alpha-linked acidic dipeptidase produces an antinociceptive effect during the rat formalin test but not during the hot plate test.
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Affiliation(s)
- T Yamamoto
- Department of Anesthesiology, School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba-shi, 260-8670, Chiba, Japan.
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Lea PM, Wroblewska B, Sarvey JM, Neale JH. beta-NAAG rescues LTP from blockade by NAAG in rat dentate gyrus via the type 3 metabotropic glutamate receptor. J Neurophysiol 2001; 85:1097-106. [PMID: 11247980 DOI: 10.1152/jn.2001.85.3.1097] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
N-Acetylaspartylglutamate (NAAG) is an agonist at the type 3 metabotropic glutamate receptor (mGluR3), which is coupled to a Gi/o protein. When activated, the mGluR3 receptor inhibits adenylyl cyclase and reduces the cAMP-mediated second-messenger cascade. Long-term potentiation (LTP) in the medial perforant path (MPP) of the hippocampal dentate gyrus requires increases in cAMP. The presence of mGluR3 receptors and NAAG in neurons of the dentate gyrus suggests that this peptide transmitter may inhibit LTP in the dentate gyrus. High-frequency stimulation (100 Hz; 2 s) of the MPP resulted in LTP of extracellularly recorded excitatory postsynaptic potentials at the MPP-granule cell synapse of rat hippocampal slices. Perfusion of the slice with NAAG (50 and 200 microM) blocked LTP. Neither 50 nor 200 microM NAAG produced N-methyl-D-aspartate receptor currents in the granule cells of the acute hippocampal slice. The group II mGluR antagonist ethyl glutamate (100 microM) and a structural analogue of NAAG, beta-NAAG (100 microM), prevented the blockade of LTP by NAAG. Paired-pulse depression of the excitatory postsynaptic potential at 20- and 80-ms interpulse intervals (IPI) was not affected by NAAG or beta-NAAG. beta-NAAG did not affect inositol trisphosphate production stimulated by the agonist glutamate in cells expressing the group I mGluR1alpha or mGluR5. beta-NAAG blocked the decrease in forskolin-stimulated cAMP by the group II mGluR agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) but not the group III mGluR agonist L(+)-2-amino-4-phosphonobutyric acid in cerebellar granule cells. In cells transfected with mGluR3, but not mGluR2, beta-NAAG blocked forskolin-stimulated cAMP responses to glutamate, NAAG, the nonspecific group I, II agonist trans-ACPD, and the group II agonist DCG-IV. We conclude that beta-NAAG is a selective mGluR antagonist capable of differentiating between mGluR2 and mGluR3 subtypes and that the mGluR3 receptor functions to regulate activity-dependent synaptic potentiation in the hippocampus.
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MESH Headings
- Animals
- Cells, Cultured
- Cricetinae
- Dentate Gyrus/cytology
- Dentate Gyrus/drug effects
- Dentate Gyrus/metabolism
- Dipeptides/chemistry
- Dipeptides/metabolism
- Dipeptides/pharmacology
- Dose-Response Relationship, Drug
- Excitatory Amino Acid Agonists
- Excitatory Amino Acid Antagonists/pharmacology
- Excitatory Postsynaptic Potentials/drug effects
- Long-Term Potentiation/drug effects
- Long-Term Potentiation/physiology
- Male
- Neurotransmitter Agents/metabolism
- Patch-Clamp Techniques
- Presynaptic Terminals/drug effects
- Presynaptic Terminals/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptors, AMPA/drug effects
- Receptors, AMPA/metabolism
- Receptors, Metabotropic Glutamate/agonists
- Receptors, Metabotropic Glutamate/antagonists & inhibitors
- Receptors, Metabotropic Glutamate/genetics
- Receptors, Metabotropic Glutamate/metabolism
- Receptors, N-Methyl-D-Aspartate/drug effects
- Receptors, N-Methyl-D-Aspartate/metabolism
- Stereoisomerism
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Affiliation(s)
- P M Lea
- Department of Physiology, Uniformed Services University, Bethesda, Maryland 20814-4799, USA
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31
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Zhao J, Ramadan E, Cappiello M, Wroblewska B, Bzdega T, Neale JH. NAAG inhibits KCl-induced [3H]-GABA release via mGluR3, cAMP, PKA and L-type calcium conductance. Eur J Neurosci 2001. [DOI: 10.1046/j.1460-9568.2001.01396.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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32
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Slusher BS, Thomas A, Paul M, Schad CA, Ashby CR. Expression and acquisition of the conditioned place preference response to cocaine in rats is blocked by selective inhibitors of the enzyme N-acetylated-?-linked-acidic dipeptidase (NAALADASE). Synapse 2001; 41:22-8. [PMID: 11354010 DOI: 10.1002/syn.1056] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In this study we examined the effect of 2-(phosphonomethyl)pentanedioic acid (2-PMPA) and GPI 5693, selective inhibitors of the enzyme N-Acetylated-alpha-Linked-Acidic Dipeptidase (NAALADase; glutamate carboxypeptidase II; EC no. 3.4.17.21), which cleaves glutamate from the dipeptide N-acetyl-aspartyl-glutamate (NAAG), on the conditioned place preference (CPP) response to cocaine in male rats. The i.p. administration of 15 mg/kg of cocaine produced a significant CPP response. The acquisition and expression of the CPP response to cocaine was blocked by the i.p. administration of 100 mg/kg of 2-PMPA and the p.o. administration of 30 mg/kg of GPI 5693. In contrast, neither 2-PMPA nor GPI 5693 produced a CPP or conditioned place aversion response when administered alone. Furthermore, neither 2-PMPA or GPI 5693 altered the expression of the CPP response to food. These results indicate that NAALADase inhibitors block the incentive motivational value of cocaine, suggesting that such agents may be of use in treating cue-induced craving in cocaine addicts.
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Affiliation(s)
- B S Slusher
- Department of Research, Guilford Pharmaceuticals, Inc., Baltimore, Maryland, USA
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33
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Shave E, Pliss L, Lawrance ML, FitzGibbon T, Stastny F, Balcar VJ. Regional distribution and pharmacological characteristics of [3H]N-acetyl-aspartyl-glutamate (NAAG) binding sites in rat brain. Neurochem Int 2001; 38:53-62. [PMID: 10913688 DOI: 10.1016/s0197-0186(00)00045-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Autoradiographical studies revealed that 10 nM [3H]N-acetyl-aspartyl-glutamate (NAAG) labelled grey matter structures, particularly in the hippocamus, cerebral neocortex, striatum, septal nuclei and the cerebellar cortex. The binding was inhibited by (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)-glycine (DCG IV), an agonist at group II metabotropic glutamate receptors (mGluR II). (RS)-alpha-Methyl-4-tetrazolylphenylglycine (MTPG), (RS)-alpha-cyclopropyl-4-phosphonoglycine (CPPG) and (RS)-alpha-methylserine-O-phosphate monophenyl ester (MSOPPE), all antagonists at mGluR II and mGluR III, also inhibited [3H]NAAG binding. Other inhibitors were (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate (ACPD), a broad-spectrum mGluR agonist with preference for groups I and II and the mGluR I agonists/mGluR II antagonists (S)-3-carboxy-4-hydroxyphenylglycine (3,4-CHPG) and (S)-4-carboxy-3-hydroxyphenylglycine (4,3-CHPG). Neither the mGluR I specific agonist (S)-dihydroxyphenylglycine nor any of the ionotropic glutamate receptor ligands such as kainate, AMPA and MK-801 had strong effects (except for the competitive NMDA antagonist CGS 19755, which produced 20-40% inhibition at 100 microM) suggesting that, at low nM concentrations, [3H]NAAG binds predominantly to metabotropic glutamate receptors, particularly those of the mGluR II type. Several studies have indicated that NAAG can interact with mGluR II and the present study supports this notion by demonstrating that sites capable of binding NAAG at low concentrations and displaying pharmacological characteristics of mGluR II exist in the central nervous tissue. Furthermore, the results show that autoradiography of [3H]NAAG binding can be used to quantify the distribution of such sites in distinct brain regions and study their pharmacology at the same time.
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Affiliation(s)
- E Shave
- Department of Anatomy and Histology, The University of Sydney, NSW, Australia
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34
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Abstract
Sensitization to cocaine has been attributed to alterations in excitatory amino acid and dopamine neurotransmission in the mesolimbic system. The present study sought to determine whether inhibition of NAALADase, an enzyme that cleaves glutamate from the endogenous neuropeptide, N-acetyl-aspartyl-glutamate (NAAG), attenuates sensitization to the psychomotor stimulant effects of cocaine. Rats received daily injections of cocaine (20.0 mg/kg/day; i.p.) or saline for 5 days. Fifteen minutes prior to these injections they received an i.p. injection of the NAALADase inhibitor, 2-PMPA (50.0-100 mg/kg), or vehicle. Locomotor activity and stereotypy produced by a challenge dose of cocaine (15.0 mg/kg) were assessed 3 days later. Acute cocaine administration increased locomotor activity in control animals. In animals with a prior history of cocaine administration, the behavioral response to cocaine was significantly enhanced. In animals that had received 2-PMPA in combination with cocaine, the enhancement of cocaine-induced locomotor activity was attenuated. No alteration in cocaine-evoked activity was observed in animals that had received once daily injections of 2-PMPA, alone. Acute administration of 2-PMPA also did not modify saline-induced locomotor activity or activity produced by an acute cocaine challenge. These data demonstrate that NAALADase inhibition attenuates the development of sensitization to the locomotor-activating effects of cocaine. Furthermore, this action cannot be attributed to an antagonism of the acute effects of cocaine.
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Affiliation(s)
- T S Shippenberg
- Integrative Neuroscience Unit, Behavioral Neuroscience Laboratory, NIH/NIDA Intramural Research Program, Baltimore, Maryland 21224, USA.
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35
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McKinzie DL, Li TK, McBride WJ, Slusher BS. NAALADase inhibition reduces alcohol consumption in the alcohol-preferring (P) line of rats. Addict Biol 2000; 5:411-6. [PMID: 20575858 DOI: 10.1111/j.1369-1600.2000.tb00209.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
N-acetyl-aspartyl-glutamate (NAAG) is a major peptide component of the brain, with millimolar tissue levels of 0.1-5 nmol/mg wet weight. NAAG is hydrolyzed by the enzyme N-acetylated alpha-linked acidic dipeptidase (NAALADase; glutamate carboxypeptidase II; EC no. 3.4.17.21) to N-acetyl-aspartate (NAA) and glutamate. Recently, a potent and selective NAALADase inhibitor termed 2-(phosphonomethyl)pentanedioic acid (2-PMPA) was identified that has a 300 pM Ki for NAALADase inhibition. Given the accumulating evidence indicating an important role of the glutamate system in alcoholism and dependence, the objective of this study was to evaluate the effects of systemic administration of 2-PMPA (50, 100 and 200 mg/kg; i.p.) upon the ethanol intakes of alcohol-preferring (P) rats. Female P rats (n = 8) received daily 1-hour scheduled access to a 10% (v/v) ethanol. In a within-subjects design, 2-PMPA treatments were tested once a week. Baseline ethanol drinking consisted of the mean of the 3 days prior to testing in which saline injections were given. Results indicated that, whereas the 200 mg/kg dose of 2-PMPA had no effect on ethanol intake, both the 50 and 100 mg/kg doses significantly reduced ethanol consumption by approximately 25% (p < 0.05) during the 1-hour access period. Body weights and 24-hour water intakes were not altered at any of the doses. These data suggest that the NAAG/NAALADase system may be involved in neuronal systems regulating alcohol-drinking behavior.
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Affiliation(s)
- D L McKinzie
- Department of Psychiatry, Indiana University School of Medicine, Indianopolis, IN, USA
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36
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Neale JH, Bzdega T, Wroblewska B. N-Acetylaspartylglutamate: the most abundant peptide neurotransmitter in the mammalian central nervous system. J Neurochem 2000; 75:443-52. [PMID: 10899918 DOI: 10.1046/j.1471-4159.2000.0750443.x] [Citation(s) in RCA: 278] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the progress of science, as in life, timing is important. The acidic dipeptide, N-acetylaspartylglutamate (NAAG), was discovered in the mammalian nervous system in 1965, but initially was not considered to be a neurotransmitter candidate. In the mid-1980s, a few laboratories revisited the question of NAAG's role in the nervous system and pursued hypotheses regarding its function that ranged from a precursor for the transmitter pool of glutamate to a direct role as a peptide transmitter. Since that time, NAAG has been tested against nearly all of the established criteria for identification of a neurotransmitter. It successfully meets each of these tests, including a concentrated presence in neurons and synaptic vesicles, release from axon endings in a calcium-dependent manner following initiation of action potentials, and extracellular hydrolysis by membrane-bound peptidase activity. NAAG is the most prevalent and widely distributed neuropeptide in the mammalian nervous system. NAAG activates NMDA receptors with a low potency that may vary among receptor subtypes, and it is a highly selective agonist at the type 3 metabotropic glutamate receptor (mGluR3). Acting through this receptor, NAAG reduces cyclic AMP levels, decreases voltage-dependent calcium conductance, suppresses excitotoxicity, influences long-term potentiation and depression, regulates GABA(A) receptor subunit expression, and inhibits synaptic release of GABA from cortical neurons. Cloning of peptidase activities against NAAG provides opportunities to study the cellular and molecular mechanisms by which synaptic NAAG peptidase activity is controlled. Given the codistribution of this peptide with a spectrum of traditional transmitters and its ability to activate mGluR3, we speculate that one role for NAAG following synaptic release is the activation of metabotropic autoreceptors that inhibit subsequent transmitter release. A second role is the production of extracellular glutamate following NAAG hydrolysis.
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Affiliation(s)
- J H Neale
- Department of Biology, Georgetown University, Washington, D.C., USA.
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37
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Slusher BS, Vornov JJ, Thomas AG, Hurn PD, Harukuni I, Bhardwaj A, Traystman RJ, Robinson MB, Britton P, Lu XC, Tortella FC, Wozniak KM, Yudkoff M, Potter BM, Jackson PF. Selective inhibition of NAALADase, which converts NAAG to glutamate, reduces ischemic brain injury. Nat Med 1999; 5:1396-402. [PMID: 10581082 DOI: 10.1038/70971] [Citation(s) in RCA: 227] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We describe here a new strategy for the treatment of stroke, through the inhibition of NAALADase (N-acetylated-alpha-linked-acidic dipeptidase), an enzyme responsible for the hydrolysis of the neuropeptide NAAG (N-acetyl-aspartyl-glutamate) to N-acetyl-aspartate and glutamate. We demonstrate that the newly described NAALADase inhibitor 2-PMPA (2-(phosphonomethyl)pentanedioic acid) robustly protects against ischemic injury in a neuronal culture model of stroke and in rats after transient middle cerebral artery occlusion. Consistent with inhibition of NAALADase, we show that 2-PMPA increases NAAG and attenuates the ischemia-induced rise in glutamate. Both effects could contribute to neuroprotection. These data indicate that NAALADase inhibition may have use in neurological disorders in which excessive excitatory amino acid transmission is pathogenic.
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Affiliation(s)
- B S Slusher
- Guilford Pharmaceuticals, Department of Research, Baltimore, Maryland 21224, USA.
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38
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Goff DC, Bagnell AL, Perlis RH. Glutamatergic Augmentation Strategies for Cognitive Impairment in Schizophrenia. Psychiatr Ann 1999. [DOI: 10.3928/0048-5713-19991101-11] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Tsai G, van Kammen DP, Chen S, Kelley ME, Grier A, Coyle JT. Glutamatergic neurotransmission involves structural and clinical deficits of schizophrenia. Biol Psychiatry 1998; 44:667-74. [PMID: 9798069 DOI: 10.1016/s0006-3223(98)00151-6] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Phencyclidine and ketamine induce a syndrome closely resembling schizophrenia due to their blockade of N-methyl-D-aspartate (NMDA) receptor. These findings suggested that some aspects of schizophrenia are associated with decreased NMDA--glutamatergic function. We hypothesized that structural and symptomatic deficits in schizophrenia are related to glutamatergic neurotransmission. METHODS We studied the relationships among cerebrospinal fluid (CSF) glutamatergic markers, clinical presentation of schizophrenia, and CT parameters of brain structure in drug-free schizophrenics. RESULTS We found no significant differences between patients with schizophrenia and controls in CSF glutamatergic markers. When patients with schizophrenia were considered as a group, significant negative correlations between glutamatergic markers and brain structural measures as well as clinical measures were observed. Cluster analysis reveals a group of lower indices of glutamatergic neurotransmission, and more prominent thought disorder as well as ventricular enlargement, and a group with increased glutamate level. CONCLUSIONS The findings support the hypothesis that altered glutamatergic neurotransmission plays a role in the brain structure and the clinical symptoms of schizophrenia.
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Affiliation(s)
- G Tsai
- Laboratory of Molecular and Developmental Neuroscience, Harvard Medical School, Charlestown, Massachusetts, USA
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40
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Bruno V, Wroblewska B, Wroblewski JT, Fiore L, Nicoletti F. Neuroprotective activity of N-acetylaspartylglutamate in cultured cortical cells. Neuroscience 1998; 85:751-7. [PMID: 9639269 DOI: 10.1016/s0306-4522(97)00531-9] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The endogenous dipeptide, alpha-N-acetylaspartylglutamate behaves as a partial agonist of N-methyl-D-aspartate receptors, but can also activate metabotropic glutamate receptors, with a high degree of selectivity for the metabotropic glutamate receptor 3 subtype. Knowing that agonists of group-II metabotropic glutamate receptors (i.e. of mGlu2 and -3 receptors) are neuroprotective, we have examined the neuroprotective activity of alpha-N-acetylaspartylglutamate in mixed cultures of mouse cortical cells exposed to a toxic pulse with N-methyl-D-aspartate. Alpha-N-acetylaspartylglutamate co-applied with N-methyl-D-aspartate was neuroprotective, but its action was insensitive to the selective group-II metabotropic glutamate receptor antagonist, ethylglutamate. Protection was instead antagonized by ethylglutamate when alpha-N-acetylaspartylglutamate was applied to the cultures immediately after the N-methyl-D-aspartate pulse, a condition in which there was no direct competition between alpha-N-acetylaspartylglutamate and N-methyl-D-aspartate at the level of N-methyl-D-aspartate receptors. alpha-N-acetylaspartylglutamate was highly neuroprotective when transiently applied to pure cultures of cortical astrocytes and the conditioned medium, collected 20 h later, was transferred to sister mixed cultures challenged with N-methyl-D-aspartate. This particular form of neuroprotection was attenuated or abolished when astrocytes where exposed to alpha-N-acetylaspartylglutamate in the presence of the group-II metabotropic glutamate receptor antagonists ethylglutamate or (2S, 1'S,2'S,3'R)-2-(2'-carboxy-3'-phenylcyclopropyl)glycine, but not in the presence of the N-methyl-D-aspartate receptor antagonist, D-2-amino-5-phosphonopentanoate. These results indicate that alpha-N-acetylaspartylglutamate induces neuroprotective effects in culture, which are mediated, at least in part, by the activation of glial metabotropic glutamate receptor 3 receptors.
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Affiliation(s)
- V Bruno
- I.N.M. Neuromed, Pozzilli, Italy
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41
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Luthi-Carter R, Berger UV, Barczak AK, Enna M, Coyle JT. Isolation and expression of a rat brain cDNA encoding glutamate carboxypeptidase II. Proc Natl Acad Sci U S A 1998; 95:3215-20. [PMID: 9501243 PMCID: PMC19722 DOI: 10.1073/pnas.95.6.3215] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
N-acetylated alpha-linked acidic dipeptidase (NAALADase) hydrolyzes acidic peptides, such as the abundant neuropeptide N-acetyl-alpha-L-aspartyl-L-glutamate (NAAG), thereby generating glutamate. Previous cDNA cloning efforts have identified a candidate rat brain NAALADase partial cDNA, and Northern analyses have identified a family of related RNA species that are found only in brain and other NAALADase-expressing cells. In this report, we describe the cloning of a set of rat brain cDNAs that describe a full-length NAALADase mRNA. Transient transfection of a full-length cDNA into the PC3 cell line confers NAAG-hydrolyzing activity that is sensitive to the NAALADase inhibitors quisqualic acid and 2-(phosphonomethyl)glutaric acid. Northern hybridization detects the expression of three similar brain RNAs approximately 3,900, 3,000, and 2,800 nucleotides in length. In situ hybridization histochemistry shows that NAALADase-related mRNAs have an uneven regional distribution in rat brain and are expressed predominantly by astrocytes as demonstrated by their colocalization with the astrocyte-specific marker glial fibrillary acidic protein.
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Affiliation(s)
- R Luthi-Carter
- Department of Psychiatry, Massachusetts General Hospital-East, Charlestown, MA 02129, USA
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42
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Abstract
N-Acetylaspartylglutamate (NAAG) is a neuropeptide found in millimolar concentrations in brain that is localized to subpopulations of glutamatergic, cholinergic, GABAergic, and noradrenergic neuronal systems. NAAG is released upon depolarization by a Ca(2+)-dependent process and is an agonist at mGluR3 receptors and an antagonist at NMDA receptors. NAAG is catabolized to N-acetylaspartate and glutamate primarily by glutamate carboxypeptidase II, which is expressed on the extracellular surface of astrocytes. The levels of NAAG and the activity of carboxypeptidase II are altered in a regionally specific fashion in several neuropsychiatric disorders.
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Affiliation(s)
- J T Coyle
- Department of Psychiatry, Harvard Medical School, Belmont, Massachusetts 02178, USA.
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43
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Abstract
The excitatory amino acids, glutamate and aspartate, are of interest to schizophrenia research because of their roles in neurodevelopment, neurotoxicity and neurotransmission. Recent evidence suggests that densities of glutamatergic receptors and the ratios of subunits composing these receptors may be altered in schizophrenia, although it is unclear whether these changes are primary or compensatory. Agents acting at the phencyclidine binding site of the NMDA receptor produce symptoms of schizophrenia in normal subjects, and precipitate relapse in patients with schizophrenia. The improvement of negative symptoms with agents acting at the glycine modulatory site of the NMDA receptor, as well as preliminary evidence that clozapine may differ from conventional neuroleptic agents in its effects on glutamatergic systems, suggest that clinical implications may follow from this model. While geriatric patients may be at increased risk for glutamate-mediated neurotoxicity, very little is known about the specific relevance of this model to geriatric patients with schizophrenia.
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Affiliation(s)
- D C Goff
- Psychotic Disorders Program, Massachusetts General Hospital, Harvard Medical School, Boston, USA.
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44
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Passani LA, Vonsattel JP, Coyle JT. Distribution of N-acetylaspartylglutamate immunoreactivity in human brain and its alteration in neurodegenerative disease. Brain Res 1997; 772:9-22. [PMID: 9406950 DOI: 10.1016/s0006-8993(97)00784-1] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The dipeptide N-acetylaspartylglutamate (NAAG) may be involved in the process of glutamatergic signaling by both acting at glutamate receptors and as a glutamate protransmitter. In the present study we determined the cellular localization and distribution of NAAG-like immunoreactivity (NAAG-LI) in normal human brain and in neurodegenerative disorders to ascertain the degree of NAAG's colocalization to putative glutamatergic pathways. Immunohistochemistry with an antibody against NAAG was performed on control, Huntington's disease (HD) and Alzheimer's disease (AD) human autopsy and biopsy brain sections from the cerebral cortex, hippocampus, amygdala, neostriatum, brainstem and spinal cord. In normal human brain, NAAG-LI was widespread localized to putative glutamatergic pyramidal neurons of the cerebral cortex and hippocampus. Punctate NAAG-LI was present in areas known to receive neuronal glutamatergic input, such as layer IV of the cerebral cortex, striatal neuropil, and the outer portion of the molecular layer of the hippocampal dentate gyrus. In the two pathologic brain regions examined, the HD neostriatum and the AD temporal cortex, we observed a widespread loss of NAAG-LI neurons. In addition NAAG-LI reactive microglia surrounding plaques were seen in AD temporal cortex but not in the HD striatum. Our results suggest that NAAG is substantially localized to putative glutamatergic pathways in human brain and that NAAG-LI neurons are vulnerable to the neurodegenerative process in HD and AD.
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Affiliation(s)
- L A Passani
- Laboratory of Molecular and Developmental Neuroscience, Massachusetts General Hospital, Charlestown, USA
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45
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Passani LA, Vonsattel JP, Carter RE, Coyle JT. N-acetylaspartylglutamate, N-acetylaspartate, and N-acetylated alpha-linked acidic dipeptidase in human brain and their alterations in Huntington and Alzheimer's diseases. MOLECULAR AND CHEMICAL NEUROPATHOLOGY 1997; 31:97-118. [PMID: 9376025 DOI: 10.1007/bf02815236] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
There is mounting evidence, primarily from research in experimental animals, that the dipeptide N-acetylaspartylglutamate (NAAG) and its metabolic enzyme, N-acetylated alpha-linked acid dipeptidase (NAALADase), are involved in glutamatergic neurotransmission. Previous studies in neuropsychiatric disorders associated with the dysregulation of glutamatergic neurotransmission, such as schizophrenia, seizure disorders, and amyotrophic lateral sclerosis (ALS), have revealed region-specific alterations in the levels of NAAG and in the activity of NAALADase. To establish better the cellular localization of these and related parameters in human brain, we have examined their alterations in two well-characterized selective neurodengenerative disorders, Huntington Disease (HD) and Alzheimer Disease (AD). Brain regions from postmortem controls and HD- or AD-affected individuals were assayed to determine the activity of NAALADase as well as the levels of NAAG, N-acetylaspartate (NAA), and several amino acids. The relationships between changes in these neurochemical parameters and changes in neuronal and glial cell density were determined. The present report demonstrates that the decreases in the levels of NAAG and NAA and in the activity of NAALADase in AD and HD brain correlate primarily with neuronal loss. By inference, the results suggest that NAAG and NAA have primarily a neuronal localization in human brain and that there is a close relationship between NAAG and the dipeptidase NAALADase in populations of affected neurons.
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Affiliation(s)
- L A Passani
- Laboratory of Molecular and Developmental Neuroscience, Massachusetts General Hospital, Charlestown, USA
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Renno WM, Lee JH, Beitz AJ. Light and electron microscopic immunohistochemical localization of N-acetylaspartylglutamate (NAAG) in the olivocerebellar pathway of the rat. Synapse 1997; 26:140-54. [PMID: 9131773 DOI: 10.1002/(sici)1098-2396(199706)26:2<140::aid-syn5>3.0.co;2-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The inferior olive (IO) is the sole contributor of climbing fibers (CF) to the Purkinje cells of the cerebellar cortex. Although the anatomy and the connectivity between the IO and the cerebellum have been well established, there is still controversy regarding the neurotransmitter systems mediating olivocerebellar projections. The excitatory amino acids, glutamate (Glu) and aspartate (Asp), have both been considered as neurotransmitter candidates of olivocerebellar projections in the rat. More recently N-acetylaspartylglutamate (NAAG) has also been proposed as a transmitter of cerebellar climbing fibers based on biochemical and electrophysiological data. The aim of the present study was to determine whether NAAG immunoreactivity is present in the IO and CF at the light and electron microscopic levels and to quantitate the amount of immunogold labeling in olivary neurons and climbing fiber terminals containing this dipeptide. A polyclonal antisera against NAAG was utilized with a peroxidase-labeled avidin-biotin procedure to demonstrate these immunoreactive neurons in the IO at the light microscopic level. Approximately 45% of olivary neurons display NAAG-like immunoreactivity, and their distribution is unevenly clustered throughout the inferior olive. Using postembedding immunogold electron microscopy in combination with quantitative procedures, we found the highest densities of gold particles in the axonal terminals synapsing on olivary neurons (101.0 particles/microns2), in CF terminals (96.3 particles/microns2), and in some mossy fiber terminals (101.0 particles/microns2). Approximately half of the climbing fiber terminals examined were unlabeled. Moderate labeling occurred in CF axons (70.8 particles/microns2), while IO neuronal perikarya were lightly but significantly labeled (41.6 particles/microns2). The localization of NAAG in the subset of cerebellar climbing fiber terminals provides anatomical support for the hypothesis that NAAG may serve as a neurotransmitter/neuromodulator candidate in the olivocerebellar pathway.
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Affiliation(s)
- W M Renno
- Department of Anatomy, King Saud University, College of Medicine, Abha, Saudi Arabia. A03A002@SAKSU00
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Carter RE, Feldman AR, Coyle JT. Prostate-specific membrane antigen is a hydrolase with substrate and pharmacologic characteristics of a neuropeptidase. Proc Natl Acad Sci U S A 1996; 93:749-53. [PMID: 8570628 PMCID: PMC40126 DOI: 10.1073/pnas.93.2.749] [Citation(s) in RCA: 251] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
This report demonstrates that the investigational prostatic carcinoma marker known as the prostate-specific membrane antigen (PSM) possesses hydrolytic activity with the substrate and pharmacologic properties of the N-acetylated alpha-linked acidic dipeptidase (NAALADase). NAALADase is a membrane hydrolase that has been characterized in the mammalian nervous system on the basis of its catabolism of the neuropeptide N-acetylaspartylglutamate (NAAG) to yield glutamate and N-acetylaspartate and that has been hypothesized to influence glutamatergic signaling processes. The immunoscreening of a rat brain cDNA expression library with anti-NAALADase antisera identified a 1428-base partial cDNA that shares 86% sequence identity with 1428 bases of the human PSM cDNA [Israeli, R. S., Powell, C. T., Fair, W. R. & Heston, W.D.W. (1993) Cancer Res. 53, 227-230]. A cDNA containing the entire PSM open reading frame was subsequently isolated by reverse transcription-PCR from the PSM-positive prostate carcinoma cell line LNCaP. Transient transfection of this cDNA into two NAALADase-negative cell lines conferred NAAG-hydrolyzing activity that was inhibited by the NAALADase inhibitors quisqualic acid and beta-NAAG. Thus we demonstrate a PSM-encoded function and identify a NAALADase-encoding cDNA. Northern analyses identify at least six transcripts that are variably expressed in NAALADase-positive but not in NAALADase-negative rat tissues and human cell lines; therefore, PSM and/or related molecular species appear to account for NAAG hydrolysis in the nervous system. These results also raise questions about the role of PSM in both normal and pathologic prostate epithelial-cell function.
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Affiliation(s)
- R E Carter
- Department of Psychiatry, Massachusetts General Hospital-East, Charlestown 02129, USA
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Tsai G, Cork LC, Slusher BS, Price D, Coyle JT. Abnormal acidic amino acids and N-acetylaspartylglutamate in hereditary canine motoneuron disease. Brain Res 1993; 629:305-9. [PMID: 8111634 DOI: 10.1016/0006-8993(93)91335-p] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Hereditary canine spinal muscular atrophy (HCSMA) is a lower motor neuron disease found in Brittany Spaniels that shares clinical and pathological features with human amyotrophic lateral sclerosis (ALS). Since acidic excitatory amino acids and the neuropeptide N-acetyl-aspartyl-glutamate (NAAG) are reduced in spinal cord and cerebral cortex in ALS, the levels of these substances were measured in nervous tissue in Brittany Spaniels heterozygous and homozygous for HCSMA. Significant reductions in the levels of endogenous aspartate, glutamate, N-acetylaspartate (NAA), and NAAG were found in the spinal cord in homozygous but not heterozygous HCSMA. In contrast, the activity of N-acetylated-alpha-linked-amino dipeptidase (NAALADase), an enzyme that cleaves NAAG into NAA and Glu, was significantly increased. None of these parameters was affected in the motor cortex or occipital cortex. Since NAA and NAAG are highly concentrated in motoneurons, they may play a role in the pathogenesis of motor neuron disease.
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Affiliation(s)
- G Tsai
- Department of Psychiatry, Harvard School of Medicine, Belmont, MA 02178
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Tsai G, Slusher BS, Sim L, Coyle JT. Immunocytochemical distribution of N-acetylaspartylglutamate in the rat forebrain and glutamatergic pathways. J Chem Neuroanat 1993; 6:277-92. [PMID: 7903856 DOI: 10.1016/0891-0618(93)90033-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
N-acetylaspartylglutamate (NAAG) is an acidic dipeptide found in high concentration throughout the rat central nervous system. NAAG has been proposed as a neurotransmitter/modulator in some excitatory glutamatergic pathways where it is released by a Ca(2+)-dependent process with neuronal activity. Previous immunocytochemical studies have revealed few neurons exhibiting NAAG-like immunoreactivity (LI) in the forebrain, especially in putative glutamatergic neurons. In this study, we present a detailed map of NAAG-LI in rat forebrain utilizing a modified fixation technique that markedly enhances sensitivity. NAAG-LI is located in most of the putative glutamatergic pathways in the forebrain including pyramidal neurons in motor and sensory cortices and the hippocampal formation. Co-localization of NAAG-LI to cholinergic systems of the forebrain was quite extensive with the exception of the striatal local circuit neurons. A noteworthy feature of NAAG-LI-positive neuronal groups is that they were often configured in hierarchical relationships. For example, the pyramidal neurons of the motor cortex and the motor neurons of the brainstem and and spinal cord expressed NAAG-LI; also, several inter-related components of the limbic system stained for NAAG-LI. Taken together, these findings indicate that NAAG is a neuropeptide localized to subpopulations of neurons throughout forebrain as well as in brainstem and spinal cord.
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Affiliation(s)
- G Tsai
- Department of Neuroscience, Harvard Medical School, Belmont, MA 02178
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Li X, Orwar O, Persson J, Sandberg M, Jacobson I. Gamma-L-glutamyl-L-glutamate is an endogenous dipeptide in the rat olfactory bulb which activates N-methyl-D-aspartate receptors. Neurosci Lett 1993; 155:42-6. [PMID: 8361661 DOI: 10.1016/0304-3940(93)90669-c] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The concentration of gamma-L-glutamyl-L-glutamate (gamma-glu-glu), a potent displacer of excitatory amino acid receptor binding, and other structurally related dipeptides were determined in extracts of the rat olfactory bulb by a novel liquid chromatographic method. Whole-cell patch clamp recordings of currents from freshly isolated neurons showed that gamma-glu-glu produced inward currents at negative holding potentials, provided microM concentrations of glycine were added and no Mg(2+)-ions were present, indicating activation of N-methyl-D-aspartate receptors. Consistently, geometry optimization of gamma-glu-glu using molecular mechanics calculations, suggested a bent conformer with structural features supporting this view.
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Affiliation(s)
- X Li
- Institute of Neurobiology, University of Göteborg, Sweden
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