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Peoples RW, Ren H. Effects of ethanol on GluN1/GluN2A and GluN1/GluN2B NMDA receptor-ion channel gating kinetics. Alcohol Clin Exp Res 2022; 46:2203-2213. [PMID: 36305341 PMCID: PMC9771960 DOI: 10.1111/acer.14965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Revised: 10/20/2022] [Accepted: 10/24/2022] [Indexed: 02/01/2023]
Abstract
BACKGROUND The N-methyl-D-aspartate receptor (NMDAR) is a major molecular target of alcohol action in the central nervous system, yet many aspects of alcohol's modulation of the activity of this ion channel remain unclear. We and others have shown that ethanol inhibition of NMDAR involves alterations in gating, especially a reduction in mean open time. However, a full description of ethanol's effects on NMDAR kinetics, including fitting them to a kinetic model, has not been reported. METHODS To determine ethanol's effects on NMDAR kinetics, we used steady-state single-channel recording in outside-out patches from HEK-293 cells transfected with recombinant GluN1/GluN2A or GluN1/GluN2B NMDAR subunits. Very low glutamate concentrations were used to isolate individual activations of the receptor. RESULTS In both subunit types, ethanol, at approximate whole-cell IC50 values (156 mM, GluN2A; 150 mM, GluN2B), reduced open probability (po ) by approximately 50% and decreased mean open time without changing the frequency of opening. Open and shut time distributions exhibited two and five components, respectively; ethanol selectively decreased the time constant and relative proportion of the longer open time component. In the GluN2A subunit, ethanol increased the time constants of all but the longest shut time components, whereas in the GluN2B subunit, shut times were unchanged by ethanol. Fitting of bursts of openings (representing individual activations of the receptor) to the gating portion of a kinetic model revealed that ethanol altered two rates: the rate associated with activation of the GluN2A or GluN2B subunit, and the rate associated with the closing of the longer of the two open states. CONCLUSIONS These results demonstrate that ethanol selectively alters individual kinetic rates and thus appears to selectively affect distinct conformational transitions involved in NMDAR gating.
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Affiliation(s)
- Robert W Peoples
- Department of Biomedical Sciences, Marquette University, Milwaukee, Wisconsin, USA
| | - Hong Ren
- Biobank, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
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Lockridge A, Romero G, Harrington J, Newland B, Gong Z, Cameron A, Yuan LL. Timing-dependent reduction in ethanol sedation and drinking preference by NMDA receptor co-agonist d-serine. Alcohol 2012; 46:389-400. [PMID: 22445805 DOI: 10.1016/j.alcohol.2011.11.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Revised: 10/31/2011] [Accepted: 11/09/2011] [Indexed: 01/06/2023]
Abstract
NMDA receptors become a major contributor to acute ethanol intoxication effects at high concentrations as ethanol binds to a unique site on the receptor and inhibits glutamatergic activity in multiple brain areas. Although a convincing body of literature exists on the ability of NMDA receptor antagonists to mimic and worsen cellular and behavioral ethanol effects, receptor agonists have been less well-studied. In addition to a primary agonist site for glutamate, the NMDA receptor contains a separate co-agonist site that responds to endogenous amino acids glycine and d-serine. d-serine is both selective for this co-agonist site and potent in boosting NMDA dependent activity even after systemic administration. In this study, we hypothesized that exogenous d-serine might ameliorate some acute ethanol behaviors by opposing NMDA receptor inhibition. We injected adult male C57 mice with a high concentration of d-serine at various time windows relative to ethanol administration and monitored sedation, motor coordination and voluntary ethanol drinking. d-serine (2.7 g/kg, ip) prolonged latency to a loss of righting reflex (LoRR) and shortened LoRR duration when given 15 min before ethanol (3 g/kg) but not when it was injected with or shortly after ethanol. Blood samples taken at sedative recovery and at fixed time intervals revealed no effect of d-serine on ethanol concentration but an ethanol-induced decrease in l-serine and glycine content was prevented by acute d-serine pre-administration. d-serine had no effect on ethanol-induced (2 g/kg) rotarod deficits in young adult animals but independently and interactively degraded motor performance in a subset of older mice. Finally, a week-long series of daily ip injections resulted in a 50% decrease in free choice ethanol preference for d-serine treated animals compared to saline-injected controls in a two-bottle choice experiment.
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Affiliation(s)
- Amber Lockridge
- Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455, USA
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Trevisan L, Petrakis IL, Pittman B, Gueorguieva R, D’Souza DC, Perry E, Limoncelli D, Krystal JH. Absence of Significant Interactive Effects of High-Dose d-Cycloserine and Ethanol in Healthy Human Subjects: Preliminary Insights Into Ethanol Actions at the GlycineB Site of NMDA Glutamate Receptors. Alcohol Clin Exp Res 2007; 32:36-42. [DOI: 10.1111/j.1530-0277.2007.00543.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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5
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Smothers CT, Woodward JJ. Effects of amino acid substitutions in transmembrane domains of the NR1 subunit on the ethanol inhibition of recombinant N-methyl-D-aspartate receptors. Alcohol Clin Exp Res 2006; 30:523-30. [PMID: 16499494 DOI: 10.1111/j.1530-0277.2006.00058.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND The N-methyl-D-aspartate (NMDA) subtype of glutamate receptor is involved in a variety of processes that regulate neuronal plasticity and is an important target for the acute and chronic effects of ethanol. However, the specific sites where ethanol interacts with the receptor protein have yet to be fully elucidated. We previously demonstrated that a phenylalanine to alanine mutation in the third transmembrane domain (TM3) of the NR1 subunit decreased the ethanol inhibition of NMDA receptors expressed in HEK293 cells. In this study, we characterized the ethanol inhibition of NMDA receptors containing additional mutations within the TM3 and TM4 domains of the NR1 subunit. METHODS Site-directed mutagenesis was used to alter specific amino acid residues in the TM3 and TM4 domains of the NR1 subunit. Mutant NR1 subunits were coexpressed with the NR2A subunit in HEK293 cells and examined for alterations in ethanol sensitivity using whole-cell voltage-clamp electrophysiology. RESULTS Replacing phenylalanine at TM3 position 639 in the NR1 subunit (F639) with 9 different amino acids produced functional receptors when coexpressed with the NR2A subunit. All mutants showed a concentration-dependent inhibition by ethanol (10-100 mM), with the alanine and serine mutants being significantly less sensitive to ethanol. Amino acid substitutions at the F639 site also produced variable changes in the concentration-response relationship to glycine. However, no significant correlation between glycine EC(50) values and the magnitude of ethanol inhibition was observed. Alanine mutations at TM4 positions 813 (M813A) and 819 (L819A), but not at 817 (F817A), of the NR1 subunit enhanced ethanol inhibition. Substitution of tryptophan for TM4 residues in the NR1 subunit (positions 820-822) that are homologous to a site in the NR2A subunit shown to reduce ethanol inhibition (A825W) had no effect on ethanol sensitivity. However, these NR1 TM4 tryptophan mutants restored the ethanol inhibition of the NR1 TM3 F639A mutant to wild-type levels in a stepwise fashion. CONCLUSIONS These results indicate that the ethanol sensitivity of NMDA receptors may be regulated by discrete sites within the TM3 and TM4 domains of the NR1 subunit.
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Affiliation(s)
- C Thetford Smothers
- Department of Neurosciences, Division of Neuroscience Research and Center for Drug and Alcohol Programs, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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Hauser KF, Khurdayan VK, Goody RJ, Nath A, Saria A, Pauly JR. Selective vulnerability of cerebellar granule neuroblasts and their progeny to drugs with abuse liability. THE CEREBELLUM 2003; 2:184-95. [PMID: 14509568 PMCID: PMC4306667 DOI: 10.1080/14734220310016132] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Cerebellar development is shaped by the interplay of genetic and numerous environmental factors. Recent evidence suggests that cerebellar maturation is acutely sensitive to substances with abuse liability including alcohol, opioids, and nicotine. Assuming substance abuse disrupts cerebellar maturation, a central question is: what are the basic mechanisms underlying potential drug-induced developmental defects? Evidence reviewed herein suggests that the maturation of granule neurons and their progeny are intrinsically affected by several classes of substances with abuse liability. Although drug abuse is also likely to target directly other cerebellar neuron and glial types, such as Purkinje cells and Bergmann glia, findings in isolated granule neurons suggest that they are often the principle target for drug actions. Developmental events that are selectively disrupted by drug abuse in granule neurons and/or their neuroblast precursors include proliferation, migration, differentiation (including neurite elaboration and synapse formation), and programmed cell death. Moreover, different classes of drugs act through distinct molecular mechanisms thereby disrupting unique aspects of development. For example, drug-induced perturbations in: (i) neurotransmitter biogenesis; (ii) ligand and ion-gated receptor function and their coupling to intracellular effectors; (iii) neurotrophic factor biogenesis and signaling; and (iv) intercellular adhesion are all likely to have significant effects in shaping developmental outcome. In addition to identifying therapeutic strategies for drug abuse intervention, understanding the mechanisms by which drugs affect cellular maturation is likely to provide a better understanding of the neurochemical events that normally shape central nervous system development.
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Affiliation(s)
- Kurt F Hauser
- Department of Anatomy & Neurobiology, University of Kentucky College of Medicine, Lexington, Kentucky, 40536-0298, USA.
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Cebere A, Liljequist S. Ethanol differentially inhibits homoquinolinic acid- and NMDA-induced neurotoxicity in primary cultures of cerebellar granule cells. Neurochem Res 2003; 28:1193-9. [PMID: 12834259 DOI: 10.1023/a:1024228412198] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The potency of ethanol to inhibit N-methyl-D-aspartate (NMDA) receptor functions may depend on the subunit composition of the NMDA receptors. We used a NR2A-B subunit-selective NMDA receptor agonist, homoquinolinic acid (HQ), and a subunit-unselective agonist, NMDA, to induce neurotoxicity in cerebellar granule cells and examined the neuroprotective actions of ethanol, as well as NR2A- and NR2B-subunit selective antagonists, respectively. HQ was a more potent neurotoxic agent than NMDA, as measured by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. NR2A- and NR2B-selective NMDA receptor antagonists displayed quite similar neuroprotective potencies against the NMDA- and HQ-produced cell death, indicating that the higher potency of HQ to induce neurotoxicity cannot be simply explained by NR2A- or NR2B-subunit selectivity. As expected, ethanol (25 and 50 mM) attenuated the NMDA-induced neurotoxicity in a non-competitive manner by significantly reducing the maximum neurotoxicity produced by NMDA. By contrast, ethanol inhibited the HQ-induced neurotoxicity in a manner resembling a competitive-like interaction significantly increasing the EC50 value for HQ, without reducing the maximum neurotoxicity produced by HQ. These results suggest that HQ reveals either a novel site or a not previously observed mechanism of interaction between ethanol and NMDA receptors in rat cerebellar granule cell cultures.
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Affiliation(s)
- Aleta Cebere
- Department of Clinical Neuroscience, Division of Drug Dependence Research, Karolinska Institutet, Stockholm, Sweden
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Affiliation(s)
- Paula L Hoffman
- Department of Pharmacology C-236, University of Colorado Health Sciences Center, 4200 E. Ninth Avenue, Denver, CO 80262, USA
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Peoples RW, Ren H. Inhibition of N-methyl-D-aspartate receptors by straight-chain diols: implications for the mechanism of the alcohol cutoff effect. Mol Pharmacol 2002; 61:169-76. [PMID: 11752218 DOI: 10.1124/mol.61.1.169] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
n-Alkanol inhibition of N-methyl-D-aspartate (NMDA) receptors exhibits a "cutoff" effect: alcohols with up to eight to nine carbon atoms inhibit the receptor, whereas larger alcohols do not. This phenomenon was originally proposed to result from size exclusion; i.e., alcohols above the cutoff are too large to bind to an amphiphilic site on the receptor. In the present study, 1,Omega-diols with 3 to 14 carbon atoms inhibited NMDA-activated current in Chinese hamster ovary and human embryonic kidney 293 cells transiently expressing NR1 and NR2B NMDA receptor subunits. Results of fluctuation analysis experiments were consistent with a similar mechanism of inhibition of NMDA-activated current by alcohols and diols. The average change in apparent energy of binding of the diols caused by addition of a methylene group was 2.1 kJ/mol, which is consistent with an important role of hydrophobic interactions. Because 1,Omega-diols with 9 to 14 carbons inhibited NMDA-activated current, despite having molecular volumes exceeding that at the cutoff point for 1-alkanols, a size exclusion mechanism seems inadequate to explain the cutoff effect. A disparity in hydrophobicity values at the cutoff for alcohols and diols, however, revealed that hydrophobicity could also not entirely explain the cutoff phenomenon. From these results, it seems that the cutoff effect on NMDA receptors results primarily from the inability of long-chain alcohols to achieve adequate concentrations at their site of action due to low aqueous solubility, although other factors may also contribute to the effect.
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Affiliation(s)
- Robert W Peoples
- Unit on Cellular Neuropharmacology, Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland 20892-8115, USA.
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Peoples RW, Stewart RR. Alcohols inhibit N-methyl-D-aspartate receptors via a site exposed to the extracellular environment. Neuropharmacology 2000; 39:1681-91. [PMID: 10884550 DOI: 10.1016/s0028-3908(00)00067-8] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
N-Methyl-D-aspartate (NMDA) receptors are important CNS target sites of alcohols, but the site and mechanism of action of alcohols on NMDA receptors remains unclear. In CHO-K1 cells transfected with NR1/NR2B NMDA receptor subunits, ethanol inhibited NMDA-activated current with an IC(50) of 138 mM. Truncation of the intracellular C-terminal domain of the NR1 subunit (NR1T) did not alter ethanol sensitivity when combined with the NR2B subunit, but a similar truncation of the NR2B subunit (NR2BT) slightly enhanced ethanol sensitivity of receptors formed from coexpression with either NR1 or NR1T subunits. 1-Pentanol applied externally inhibited NMDA receptors with an IC(50) of 9.9 mM, but intracellular application of 1-pentanol (25 mM) did not alter NMDA receptor inhibition by externally applied ethanol or 1-pentanol. In addition, the amplitude of NMDA-activated current did not decrease during the time required for 1-pentanol (25 mM) to diffuse throughout the cytoplasm. Ethanol did not inhibit NMDA receptors when bath-applied in cell-attached patches or when applied to the cytoplasmic face of inside-out membrane patches. These results appear to be best explained by an action of alcohols on the NMDA receptor-channel protein, at a site located in a domain exposed to, or only accessible from, the extracellular environment.
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Affiliation(s)
- R W Peoples
- Unit on Cellular Neuropharmacology, Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, 20892-8115, Bethesda, MD 20892-8115, USA.
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Wirkner K, Poelchen W, Köles L, Mühlberg K, Scheibler P, Allgaier C, Illes P. Ethanol-induced inhibition of NMDA receptor channels. Neurochem Int 1999; 35:153-62. [PMID: 10405999 DOI: 10.1016/s0197-0186(99)00057-1] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Ethanol is a potent inhibitor of the N-methyl-D-aspartate (NMDA)-receptor subtype of glutamate receptor in a number of brain areas. The mechanism of ethanol action has been investigated by means of patch-clamp recording of ionic currents and fura-2 measurement of intracellular Ca2+ concentration in cell culture systems; the subunit composition of NMDA receptors and their influence on the effect of ethanol was determined by molecular biology methods. Ethanol does not appear to interact with NMDA either at the glutamate recognition site of the receptor, or at any of the hitherto known multiple modulatory sites, such as the glycine or polyamine site. Moreover, ethanol does not cause an open channel block by itself and fails to interact with Mg2+ at the site where it causes open channel block. The ability of ethanol to inhibit responses to NMDA is dependent on the subunit combination of NMDA receptors. The NR1/NR2A and NR1/NR2B combinations are preferentially sensitive to ethanol inhibition. Chronic treatment with ethanol leads to an increase of the NMDA receptor number at the transcriptional and posttranscriptional level; the receptor function is also facilitated. This causes withdrawal-type seizures after termination of chronic treatment with ethanol. The inhibition of NMDA receptors by ethanol leads to the depression of excitatory synaptic potentials mediated by this type of excitatory amino acid receptor. Ethanol-induced disturbances in certain regions of the brain, i.e. hippocampus, nucleus accumbens or locus coeruleus may lead to cognitive disorders or drug dependence. Brain slices containing the locus coeruleus may be used as an in vitro test system to investigate the addictive properties of ethanol.
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Affiliation(s)
- K Wirkner
- Department of Pharmacology and Toxicology, University of Leipzig, Germany
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Allgaier C, Scheibler P, Müller D, Feuerstein TJ, Illes P. NMDA receptor characterization and subunit expression in rat cultured mesencephalic neurones. Br J Pharmacol 1999; 126:121-30. [PMID: 10051128 PMCID: PMC1565789 DOI: 10.1038/sj.bjp.0702284] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/1998] [Revised: 10/05/1998] [Accepted: 10/09/1998] [Indexed: 11/09/2022] Open
Abstract
1. NMDA-induced changes in free intracellular Ca2+ concentration ([Ca2+]i) were determined in individual cultured rat mesencephalic neurones by the fura-2 method. mRNA expression encoding NMDA receptor subunits (NR1, NR2A-D) was examined by RT-PCR. 2. NMDA (1-100 microM, plus 10 microM glycine) induced a concentration-dependent increase in [Ca2+]i (EC50 = 5.7 microM). The effect of NMDA was virtually insensitive to tetrodotoxin (0.3 microM) and nitrendipine (1 microM), but dependent on extracellular Ca2+. 5,7-Dichlorokynurenic acid (10 microM), a specific antagonist at the glycine binding site on the NMDA receptor, abolished the NMDA response. 3. Memantine, an open-channel blocker, and ifenprodil, a preferential non-competitive NR1/NR2B receptor antagonist diminished the NMDA effect with an IC50 value of 0.17 and 1 microM, respectively. Ethanol at 50 and 100 mM caused about 25 and 45%-inhibition, respectively. 4. Agarose gel analysis of the PCR products followed by ethidium bromide fluorescence or CSPD chemiluminescence detection revealed an almost exclusive expression of the NR1 splice variants lacking exon (E) 5 and E22. The 3' splice form without both E21 and E22 exceeded that containing E21 by approximately 4 fold. The relative amounts of NR2A, NR2B, NR2C corresponded to approximately 1:2:1. NR2D mRNA was also detectable. 5. In conclusion, mesencephalic neurones bear ethanol-sensitive NMDA receptors which might be involved in the development of ethanol dependence and withdrawal. The high affinity of NMDA to this receptor, its sensitivity to ifenprodil and memantine may suggest that the mesencephalic NMDA receptor comprises the NR1 splice variant lacking E5, NR2B, and NR2C, respectively.
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MESH Headings
- 2-Amino-5-phosphonovalerate/pharmacology
- Animals
- Calcium/metabolism
- Calcium Channel Blockers/pharmacology
- Cells, Cultured
- Central Nervous System Depressants/pharmacology
- Dose-Response Relationship, Drug
- Ethanol/pharmacology
- Excitatory Amino Acid Agonists/pharmacology
- Excitatory Amino Acid Antagonists/pharmacology
- Fetus
- Gene Expression
- Gene Expression Regulation, Developmental
- Glycine/pharmacology
- Memantine/pharmacology
- Mesencephalon/cytology
- Mesencephalon/drug effects
- Mesencephalon/metabolism
- N-Methylaspartate/pharmacology
- Neurons/drug effects
- Neurons/metabolism
- Nitrendipine/pharmacology
- Piperidines/pharmacology
- RNA Splicing
- RNA, Messenger/drug effects
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Rats, Wistar
- Receptors, N-Methyl-D-Aspartate/drug effects
- Receptors, N-Methyl-D-Aspartate/genetics
- Receptors, N-Methyl-D-Aspartate/physiology
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Affiliation(s)
- C Allgaier
- Institut für Pharmakologie und Toxikologie, Universität Leipzig, Germany
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Faingold CL, N'Gouemo P, Riaz A. Ethanol and neurotransmitter interactions--from molecular to integrative effects. Prog Neurobiol 1998; 55:509-35. [PMID: 9670216 DOI: 10.1016/s0301-0082(98)00027-6] [Citation(s) in RCA: 201] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
There is extensive evidence that ethanol interacts with a variety of neurotransmitters. Considerable research indicates that the major actions of ethanol involve enhancement of the effects of gamma-aminobutyric acid (GABA) at GABAA receptors and blockade of the NMDA subtype of excitatory amino acid (EAA) receptor. Ethanol increases GABAA receptor-mediated inhibition, but this does not occur in all brain regions, all cell types in the same region, nor at all GABAA receptor sites on the same neuron, nor across species in the same brain region. The molecular basis for the selectivity of the action of ethanol on GaBAA receptors has been proposed to involve a combination of benzodiazepine subtype, beta 2 subunit, and a splice variant of the gamma 2 subunit, but substantial controversy on this issue currently remains. Chronic ethanol administration results in tolerance, dependence, and an ethanol withdrawal (ETX) syndrome, which are mediated, in part, by desensitization and/or down-regulation of GABAA receptors. This decrease in ethanol action may involve changes in subunit expression in selected brain areas, but these data are complex and somewhat contradictory at present. The sensitivity of NMDA receptors to ethanol block is proposed to involve the NMDAR2B subunit in certain brain regions, but this subunit does not appear to be the sole determinant of this interaction. Tolerance to ethanol results in enhanced EAA neurotransmission and NMDA receptor upregulation, which appears to involve selective increases in NMDAR2B subunit levels and other molecular changes in specific brain loci. During ETX a variety of symptoms are seen, including susceptibility to seizures. In rodents these seizures are readily triggered by sound (audiogenic seizures). The neuronal network required for these seizures is contained primarily in certain brain stem structures. Specific nuclei appear to play a hierarchical role in generating each stereotypical behavioral phases of the convulsion. Thus, the inferior colliculus acts to initiate these seizures, and a decrease in effectiveness of GABA-mediated inhibition in these neurons is a major initiation mechanism. The deep layers of superior colliculus are implicated in generation of the wild running behavior. The pontine reticular formation, substantia nigra and periaqueductal gray are implicated in generation of the tonic-clonic seizure behavior. The mechanisms involved in the recruitment of neurons within each network nucleus into the seizure circuit have been proposed to require activation of a critical mass of neurons. Achievement of critical mass may involve excess EAA-mediated synaptic neurotransmission due, in part, to upregulation as well as other phenomena, including volume (non-synaptic diffusion) neurotransmission. Effects of ETX on receptors observed in vitro may undergo amplification in vivo to allow the excess EAA action to be magnified sufficiently to produce synchronization of neuronal firing, allowing participation of the nucleus in seizure generation. GABA-mediated inhibition, which normally acts to limit excitation, is diminished in effectiveness during ETX, and further intensifies this excitation.
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Affiliation(s)
- C L Faingold
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield 62794-1222, USA
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Moraes Ferreira VM, Morato GS. d-Cycloserine Blocks the Effects of Ethanol and HA-966 in Rats Tested in the Elevated Plus-Maze. Alcohol Clin Exp Res 1997. [DOI: 10.1111/j.1530-0277.1997.tb04501.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Peoples RW, White G, Lovinger DM, Weight FF. Ethanol inhibition of N-methyl-D-aspartate-activated current in mouse hippocampal neurones: whole-cell patch-clamp analysis. Br J Pharmacol 1997; 122:1035-42. [PMID: 9401766 PMCID: PMC1565042 DOI: 10.1038/sj.bjp.0701483] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
1. The action of ethanol on N-methyl-D-aspartate (NMDA)-activated ion current was studied in mouse hippocampal neurones in culture using whole-cell patch-clamp recording. 2. Ethanol inhibited NMDA-activated current in a voltage-independent manner, and did not alter the reversal potential of NMDA-activated current. 3. Concentration-response analysis of NMDA- and glycine-activated current revealed that ethanol decreased the maximal response to both agonists without affecting their EC50 values. 4. The polyamine spermine (1 microM) increased amplitude of NMDA-activated current but did not alter the percentage inhibition of ethanol. 5. Compared to an extracellular pH of 7.0, pH 6.0 decreased and pH 8.0 increased the amplitude of NMDA-activated current, but these changes in pH did not significantly alter the percentage inhibition by ethanol. 6. The sulphydryl reducing agent dithiothreitol (2 mM) increased the amplitude of NMDA-activated current, but did not affect the percentage inhibition by ethanol. 7. Mg2+ (10, 100, 500 microM), (5, 20 microM) or ketamine (2, 10 microM) decreased the amplitude of NMDA-activated current, but did not affect the percentage inhibition by ethanol. 8. The observations are consistent with ethanol inhibiting the function of NMDA receptors by a non-competitive mechanism that does not involve several modulatory sites on the NMDA receptor-ionophore complex.
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Affiliation(s)
- R W Peoples
- Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-8205, USA
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Barrios M, Liljequist S. Developmental changes in the inhibitory actions of ethanol on glutamate-induced translocation of protein kinase C in cerebellar granule neurons. Alcohol 1997; 14:575-80. [PMID: 9401673 DOI: 10.1016/s0741-8329(97)00050-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The effects of increasing concentrations of ethanol (25-200 mM) on the enhancement of [3H]phorbol-12,13-dibutyrate ([3H]PDBu) binding produced by different glutamate receptor agonists, indicative of a translocation of the intracellular enzyme protein kinase C (PKC), were studied in rat cerebellar granule cells at 2, 4, 8, and 12 days in vitro (DIV). Glutamate-produced stimulation of [3H]PDBu binding was inhibited by 50 mM ethanol at 2 DIV, whereas higher ethanol concentrations (> 100 mM) were needed to reduce the increase of [3H]PDBu binding in cells grown for 4, 8, and 12 DIV. Ethanol significantly inhibited NMDA-stimulated [3H]PDBu binding in a concentration-dependent fashion in cells maintained in culture for 4 and 8 days, respectively, with a slightly less pronounced inhibition by ethanol (50 mM) seen in cells kept for 2 and 12 DIV. Application of higher ethanol concentrations (> 100 mM), inhibited the NMDA-induced stimulation in all cell preparations. Following kainic acid-induced enhancement of [3H]PDBu binding, ethanol (100 mM) reduced the binding only in cells maintained for 2 DIV. Even higher ethanol concentrations (200 mM) inhibited the effects of kainic acid only in cells maintained for 2 and 4 DIV, respectively. Our data suggest that various subclasses of glutamate receptors display a developmentally determined differential sensitivity to ethanol at least in cerebellar granule cells in vitro.
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Affiliation(s)
- M Barrios
- Department of Clinical Neuroscience, Karolinska Hospital, Stockholm, Sweden
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Kotlinska J, Liljequist S. The NMDA/glycine receptor antagonist, L-701,324, produces discriminative stimuli similar to those of ethanol. Eur J Pharmacol 1997; 332:1-8. [PMID: 9298919 DOI: 10.1016/s0014-2999(97)01069-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The ethanol-like discriminative stimulus properties of a novel NMDA glycine receptor antagonist, L-701,324 ((7-chloro-4-hydroxy-3-(3-phenoxy)phenyl-2-(1H)-quinolone), a polyamine receptor antagonist, eliprodil, and a non-competitive NMDA receptor antagonist, MK-801 (dizocilpine), were examined in rats trained to discriminate ethanol from vehicle in a two-lever discrimination procedure. In rats trained to discriminate ethanol from vehicle, L-701,324 and MK-801 substituted for ethanol in a dose-dependent fashion with a complete substitution noted following administration of 7.5 mg/kg L-701,324 and 0.2 mg/kg MK-801, respectively. Full substitution for ethanol was achieved with no alteration in the rate of responding. In contrast, administration of eliprodil (in doses up to 5 mg/kg) showed only a partial, but not dose-dependent, substitution for ethanol. These findings indicate that a reduction of NMDA receptor activity, produced either via a blockade of non-competitive NMDA recognition sites or of NMDA/glycine-sensitive regulatory sites, had discriminative stimulus properties that are similar to those produced by ethanol. Furthermore, the observation that the NMDA/glycine receptor antagonist, L-701,324, was a more effective substitute for ethanol than was the polyamine antagonist, eliprodil, suggests that several NMDA receptor subunits, and thus not only NMDAR2B receptor subunits, are of importance for the discriminative stimulus effects of ethanol.
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Affiliation(s)
- J Kotlinska
- Department of Clinical Neuroscience, Karolinska Hospital, Stockholm, Sweden
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