Ethanol sensitivity of NMDA receptors (original) (raw)
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British Journal of Pharmacology, 2007
Background and purpose: NMDA receptors are important molecular targets of ethanol action in the CNS. Previous studies have identified a site in membrane-associated domain 3 (M3) of the NR1 subunit and two sites in M4 of the NR2A subunit that influence alcohol action; the sites in NR2A M4 also regulate ion channel gating. The purpose of this study was to determine whether mutations at the site in the NR2A subunit corresponding to the NR1 M3 site influence alcohol action and ion channel gating. Experimental approach: We investigated the effects of mutations at phenylalanine (F) 637 of the NR2A subunit using wholecell and single-channel patch-clamp electrophysiological recording in transiently-transfected HEK 293 cells. Key results: Mutations at F637 in the NR2A subunit altered peak and steady-state glutamate EC 50 values, maximal steady-state to peak current ratios (I ss :I p), mean open time, and ethanol IC 50 values. Differences in glutamate potency among the mutants were not due to changes in desensitization. Ethanol IC 50 values were significantly correlated with glutamate EC 50 values, but not with maximal I ss :I p or mean open time. Ethanol IC 50 values were linearly and inversely related to molecular volume of the substituent. Conclusions and implications: These results demonstrate that NR2A(F637) influences NMDA receptor affinity, ion channel gating, and ethanol sensitivity. The changes in NMDA receptor affinity are likely to be the result of altered ion channel gating. In contrast to the cognate site in the NR1 subunit, the action of ethanol does not appear to involve occupation of a critical volume at NR2A(F637).
Alcohol, 1990
The actions of glutamate, the major excitatory amino acid in the CNS, are mediated by three receptor subtypes: kainate, quisqualate and N-methyl-D-aspartate (NMDA) receptors. Ethanol, in vitro, is a potent and selective inhibitor of the actions of agonists at the NMDA receptor. Following chronic ethanol ingestion, the number of NMDA receptor-ion channel complexes in certain brain areas is increased. This increase may contribute to the generation of ethanol withdrawal seizures, since administration of an NMDA receptor antagonist can reduce these seizures. The results suggest that certain acute behavioral effects of ethanol, such as effects on memory, as well as certain aspects of ethanol withdrawal, may involve the NMDA receptor. Ethanol NMDA receptor Glutamate Ethanol withdrawal seizures MK-801 binding Cyclic GMP Calcium influx
British Journal of Pharmacology, 2016
Background and purpose: The N-methyl-D-aspartate (NMDA) receptor is an important target of alcohol action in the brain. Recent studies in this laboratory have demonstrated that alcohol-sensitive positions in the intersubunit interfaces of the M3 and M4 domains of GluN1 and GluN2A subunits interact with respect to ethanol sensitivity and receptor kinetics, and that alcohol-sensitive positions in the M domains of GluN2A and GluN2B subunits differ. In this study we tested for interactions among alcoholsensitive positions at the M domain intersubunit interfaces in GluN1/GluN2B NMDA receptors. Experimental approach: We used whole-cell patch-clamp recording in tsA201 cells expressing tryptophan substitution mutants at ethanol-sensitive NOT THE PUBLISHED VERSION; this is the author's final, peer-reviewed manuscript.
Ethanol-induced inhibition of NMDA receptor channels
Neurochemistry International, 1999
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
Behavioural Brain Research, 2014
h i g h l i g h t s • Repeated ethanol (EtOH) leads to increases in locomotor activity (sensitization). • High sensitized (HS) and low sensitized (LS) mice respond differently to EtOH. • LS mice showed brain-wide increases in NMDA NR2A expression compared to controls. • LS mice also had greater NR1 expression in the accumbens compared to HS mice. • No changes in NR1, NR2A or NR2B were seen 14 days after final EtOH injection.
Different sites of alcohol action in the NMDA receptor GluN2A and GluN2B subunits
Neuropharmacology, 2015
The NMDA receptor is a major target of alcohol action in the CNS, and recent behavioral and cellular studies have pointed to the importance of the GluN2B subunit in alcohol action. We and others have previously characterized four amino acid positions in the third and fourth membrane-associated (M) domains of the NMDA receptor GluN2A subunit that influence both ion channel gating and alcohol sensitivity. In this study, we found that substitution mutations at two of the four corresponding positions in the GluN2B subunit, F637 and G826, influence ethanol sensitivity and ion channel gating. Because position 826 contains a glycine residue in the native protein, we focused our attention on GluN2B(F637). Substitution mutations at GluN2B(F637) significantly altered ethanol IC50 values, glutamate EC50 values for peak (Ip) and steady-state (Iss) current, and steady-state to peak current ratios (Iss:Ip). Changes in apparent glutamate affinity were not due to agonist trapping in desensitized st...
NMDA-receptor antagonists block the development of rapid tolerance to ethanol in mice
Addiction Biology, 1998
Several studies have emphasized the role of learning in the development of rapid and chronic tolerances. Recently, it was shown that the NMDA antagonists MK-801(dizocilpine) and ketamine block the development of tolerance to ethanol in rats submitted to tilt-plane apparatus. The present study examines the generality of this inhibition using mice submitted to the rota-rod test. Mice were tested in the rota-rod apparatus at 5, 10 and 15 minutes after intraperitoneal ethanol injections. The first experiment evaluated the time course of acute effects of different doses of ethanol (1.0-2.25 g/kg) in the rota-rod test. In the second experiment, the most effective dose of ethanol to produce rapid tolerance (RT) was determined. Mice were injected on day 1 with ethanol or saline and tested on the rota-rod. After 24 hours, all groups were injected with the same doses of ethanol and tested. The third experiment investigated whether ketamine (1.0-5.0 mg/kg) injected before ethanol on day 1 influenced the development of RT to ethanol. The last experiment compared the actions of the (+) and (-)MK-801 isomers (0.015-0.060 mg/kg) on RT to ethanol. Maximum motor impairment was obtained 5 minutes after ethanol injections. Pretreatment of animals with ketamine (2.5 and 5 mg/kg) or with (+)MK-801 (0.030 and 0.060 mg/kg) significantly blocked the development of RT. The (-)MK-801 isomer did not affect RT, suggesting that the blockade by MK-801 is stereospecific. These results confirm and extend previous studies showing that NMDA receptor antagonists block RT to the motor impairment produced by ethanol in other animals tested in different models.
NMDA Receptor Antagonism and the Ethanol Intoxication Signal
Annals of The New York Academy of Sciences, 2003
Abstract: This paper reviews clinical evidence suggesting that antagonism of the N-methyl-d-aspartate subtype of glutamate receptors by ethanol may convey an important component of the ethanol intoxication signal, that is, subjective and objective responses associated with the consumption of a large amount of ethanol. It will then review recent evidence that two phenotypes associated with increased risk for heavy alcohol consumption, recovering ethanol-dependent patients, and healthy individuals with a family history of alcohol dependence, exhibit reduced sensitivity to the dysphoric consequences of administration of the NMDA receptor antagonist, ketamine. Each of these groups displays reduced sensitivity to a potentially important response that might normally trigger the cessation of ethanol consumption. These data raise the possibility that alterations in NMDA receptor function that reduce the response to the NMDA antagonist component of ethanol may increase the risk for heavy drinking. This hypothesis is consistent with growing evidence that NMDA receptor antagonists may play a role in the treatment of alcoholism by suppressing alcohol withdrawal, reducing the development or expression of alcohol tolerance, or preventing or reversing the sensitiziation to ethanol effects.
British Journal of Pharmacology, 2009
Background and purpose: Alcohol produces its behavioural effects in part due to inhibition of N-methyl-d-aspartate (NMDA) receptors in the CNS. Previous studies have identified amino acid residues in membrane-associated domains 3 (M3) and 4 (M4) of the NMDA receptor that influence ethanol sensitivity. In addition, in other alcohol-sensitive ion channels, sedativehypnotic agents have in some cases been shown to act at sites distinct from the sites of ethanol action. In this study, we compared the influence of mutations at these sites on sensitivity to ethanol and trichloroethanol, a sedative-hypnotic agent that is a structural analogue of ethanol. Experimental approach: We constructed panels of mutants at ethanolsensitive positions in the GluN2A (NR2A) NMDA receptor subunit and transiently expressed these mutants in human embryonic kidney 293 cells. We used whole-cell patch-clamp recording to assess the actions of ethanol and trichloroethanol in these mutant NMDA receptors. Key results: Ethanol sensitivity of mutants at GluN2A(Ala825) was not correlated with any physicochemical measures tested. Trichloroethanol sensitivity was altered in two of three ethanol-insensitive mutant GluN2A subunits: GluN2A(Phe637Trp) in M3 and GluN2A(Ala825Trp) in M4, but not GluN2A(Met823Trp). Trichloroethanol sensitivity decreased with increasing molecular volume at Phe637 or increasing hydrophobicity at Ala825 and was correlated with ethanol sensitivity at both sites. Conclusions and implications: Evidence obtained to date is consistent with a role of GluN2A(Ala825) as a modulatory site for ethanol and trichloroethanol sensitivity, but not as a binding site. Trichloroethanol appears to inhibit the NMDA receptor in a manner similar, but not identical to, that of ethanol.
NMDA Receptor Binding in Adult Rat Brain after Several Chronic Ethanol Treatment Protocols
Alcoholism: Clinical and Experimental Research, 1997
The amino acid L-glutamate is a major excitatory neurotransmitter that is involved in many CNS functions, including learning, memory, long-term potentiation, and synaptic plasticity. Acute exposures to ethanol (50 to 200 mM) have been shown to inhibit NMDA receptor responses, whereas chronic exposure to ethanol leads to adaptive supersensitiiity thought to be involved in ethanol dependence and tolerance. To investigate the effects of chronic ethanol exposure on glutamate receptor density, we examined the binding of both NMDA and non-NMDA ligands in rat brain after several chronic ethanol treatment protocols using a number of different rat strains. No increases in the binding of rH]MK-801, rH]CGP 39653, or the polyamine specific competitive antagonist, PHIifenprodil, were seen after two well-used chronic ethanol treatments. These included the 2-week liquid diet developed by Frye et al. (J. Pharmacol. €xp. Ther. 218:306414,1981) and the 4day binge treatment developed by Majchrowicz (fsychophannacologia 43:245254,1975). However, small increases in the binding of both the NMDA noncompetitive antagonist [JHIMK-801, as well as the competitive NMDA antagonist PWCGP 39653, were seen in select frontal brain regions after 3 weeks of the Walker-Freund chronic ethanol liquid diet When this chronic liquid diet treatment was extended to a period of 6 weeks, these increases in receptor binding were diminished to nonsignificant levels. The binding of the non-NMDA ligands PHIAMPA and Pwkainate were not significantly alfected by either length of Walker-Freund liquid diet exposure. When rats were treated chronically with ethanol for 30 days using the paradigm developed by Tsukamoto et al. Vlepatology 5224-232, l a) , small, but significant, increases in the binding of PHIMK-801 were seen in the CAI and dentate gyrus regions of the hippocampus. These studies indicate that robust increases in NMDA receptor binding do not occur with several chronic ethanol treatment protocols, and suggests that NMDA receptor supersensitivity during the development of tolerance and dependence to ethanol may not simply be due to changes in the density of NMDA receptors, but may invoke other mechanisms.