Michael Feyder, et al.
Received: October 29, 2009; Revised: November 9,
2009; Accepted: November 11, 2009
*Corresponding Author:Marguerite C. Camp, Section
on Behavioral Science and Genetics, Laboratory for
Integrative Neuroscience, National Institute on Alcohol
Abuse and Alcoholism, 5625 Fisher’s Lane Room 2N09,
Bethesda, MD, USA 20892-9304. Tel: +301-443-4052;
Fax: +301-480-1952; E-mail: firstname.lastname@example.org
J Med Sci 2010;30(1):003-010
Copyright © 2010 JMS
Ethanol and NMDA Receptor Interactions: Implications for
Michael Feyder1, Marguerite C. Camp1*, Andrew Holmes1, and Yi-Chyan Chen2
1Section on Behavioral Science and Genetics, Laboratory for Integrative Neuroscience,
National Institute on Alcoholism and Alcohol Abuse, NIH, Bethesda, MD, USA
2Department of Psychiatry, Tri-Service General Hospital, National Defense Medical Center,
Taipei, Taiwan, Republic of China.
Alcohol abuse and dependence constitutes a signi?cant societal and global burden; however, the basic scienti?c knowl-
edge underlying the development and maintenance of alcohol dependence is limited, resulting in few pharmacotherapies
and high rates of relapse following abstinence. A growing body of evidence supports an interaction between ethanol
(EtOH) and N-methyl-D-aspartate receptors (NMDARs) in mediating the acute and chronic effects of EtOH. The aim of
this review is to synthesize the current knowledge of this interaction on the molecular, cellular and behavioral levels and
highlight possible avenues for pharmacotherapeutic treatments.
Key words: ethanol, NMDAreceptor, neurotransmission, alcoholism
Alcohol abuse and dependence constitutes a signifi-
cant societal and global burden as a result, in part, of its
actions on the central nervous system (CNS)1. Despite
this substantial impact, the basic scientific knowledge
underlying the development and maintenance of alcohol
dependence is limited, resulting in few pharmacothera-
pies and high rates of relapse following abstinence2,3. A
growing body of evidence, however, supports an interac-
tion between ethanol (EtOH) and N-methyl-D-aspartate
receptors (NMDARs), a subclass of receptors activated
by the major excitatory neurotransmitter glutamate, in
mediating the acute and chronic effects of EtOH. The
aim of this review is to synthesize the current knowledge
of this interaction on the molecular, cellular and behav-
ioral levels and highlight possible avenues for pharmaco-
Acute EtOH and NMDARs
Initial evidence for an acute interaction between EtOH
and NMDARs was ?rst reported when electrophysiologi-
cal data revealed that EtOH dose-dependently inhibits
NMDARs at concentrations that parallel intoxication in
human subjects4. This finding was substantiated at the
behavioral level by self-administration studies demon-
strating that NMDAR antagonists substitute for EtOH
in rats5-7while human subjects report EtOH-like effects
following NMDAR antagonist administration8,9. Finally,
pretreatment with an NMDAR antagonist following ad-
ministration of EtOH prevents the development of acute
Acute EtOH and NMDAR subunits
NMDARs are composed of two obligatory NMDA
receptor 1 (NR1) subunits and at least one type of regula-
tory NR2A-D subunit or NR3A-B subunits12. The stron-
gest subunit-speci?c evidence of EtOH inhibition focuses
on the NR2A and NR2B subunits. Recombinant studies
in Xenopus oocytes demonstrate an increased inhibitory
sensitivity to EtOH in receptors expressing the NR2A
and NR2B subunits, as compared to the NR2C and
NR2D subunits, with equal sensitivity of the former two
subunits in HEK 293 cells13-15. A more detailed analysis
revealed that EtOH interacts with the fourth membrane-
associated domain of the NR2A subunit in HEK 293
cells while no such data to date has been reported for the
In neurons, however, a prominent role for the NR2B
subunit has emerged. Several studies demonstrated that
select neurons sensitive to the NR2B antagonist ifenpro-
Ethanol and NMDAneurotransmission
dil were similarly sensitive to EtOH, suggesting that the
physiological consequence of EtOH inhibition is medi-
ated by NR2B-expressing receptors in developmentally
Behavioral studies involving pharmacologically ma-
nipulated mice targeted at the NR2B subunit support its
involvement in specific acute behavioral responses to
EtOH; pretreatment with a NR2B antagonist increased
the sedative/hypnotic effect of acute EtOH in mice22,23.
Acute EtOH and NMDAR downstream signaling
NMDARs are ligand-gated ionotropic receptors that,
upon glutamate binding, are permeable to calcium ions
and initiate downstream signal transduction pathways12.
Expectedly, EtOH inhibition reduces calcium ion in?ux
and calcium-dependent synthesis of cyclic GMP24,25.
Further research, however, has detailed specific down-
stream responses to EtOH.
NMDARs interact with RhoGTPase-activating pro-
teins (RhoGAPs) to regulate dendritic spine morphol-
ogy26, and various RhoGAP splice variants in Drosophila
mediate the stimulating or sedating effects of acute EtOH
at low or high doses repectively27. Furthermore, mice
lacking Eps8, a protein that interacts with NMDARs and
regulates actin dynamics, show a diminished behavioral
response and corresponding resistance to actin remod-
eling following acute EtOH administration28. Taken
together, these results suggest that EtOH inhibition of
NMDARs influence cytoskeletal remodeling and may
contribute to the structural adaptations associated with
chronic EtOH administration29.
Quantitative trait locus and gene array analyses of
mice selectively bred for behavioral sensitivity to acute
EtOH reveal an in?uential role for, among other genes,
NMDARs and its downstream modulators. Studies report
alterations of the NR1 subunit, zinc ?nger protein 179, a
member of the RING ?nger protein family induced fol-
lowing NMDAR activation30-32, and peroxidredoxin, a
protein with antioxidant function in response to NMDAR
activation33. Collectively, these data suggest NMDARs
and various downstream molecules influence the acute
behavioral response to EtOH.
EtOH has been shown to inhibit NR2A- and NR2B-
expressing receptors, in part, by dephosphorylation via
tyrosine phosphatases34. Compensatory phosphorylation
of NMDARs, which increases open channel probability
by reducing the voltage-dependent magnesium ion block-
age35, has emerged as a common cellular mechanism, an
effect termed homeostatic phosphorylation. Following
acute EtOH administration, dopamine receptor 1 (D1)
activation of dopamine and cAMP-regulated phospho-
protein-32 kD (DARPP-32) phosphorylates the NR1 sub-
unit in the nucleus accumbens of mice36, while transient
phosphorylation of NR1 by the cAMP-dependent protein
kinase A (PKA) has been reported in the ventrolateral
medulla in the rat37. Interestingly, mice lacking various
isoforms of adenylate cyclase, the enzyme responsible
for cAMP synthesis, display abnormal PKA substrate
phosphorylation, increased sedation following EtOH
administration, and decreased voluntary EtOH consump-
tion38. These studies demonstrate an influential role of
adenylate cyclase, cAMP, DARPP-32, and NR1 homeo-
static phosphorylation in response to acute EtOH admin-
EtOH also induces regionally specific homeostatic
phosphorylation of the NR2B subunit via activation of
Fyn, a tyrosine kinase associated with EtOH dependence
in human populations39. Acute EtOH administration in-
creases NR2B tyrosine phosphorylation in the hippocam-
pus, an effect not seen in Fyn knock-out (KO) mice40,41.
The homeostatic phosphorylation by Fyn is manifested
behaviorally; Fyn KO mice show an enhanced sensitivity
to the sedative/hypnotic effects of ethanol41while an op-
posite effect is observed following overexpression of Fyn
in the forebrain42.
Acute EtOH administration also increases NR2B
phosphorylation and Fyn activation in the dorsal stria-
tum43. Given that this region is implicated in habit-based
learning and sensitive to drugs of abuse44, injection of a
Fyn inhibitor into this region reduces EtOH self-admin-
istration in rats43. Interestingly, following the removal
of EtOH from brain slice preparations, the electrophysi-
ological response of NR2B-expressing receptors in the
dorsal striatum is enhanced (termed ‘long term facilita-
tion’), providing a plausible mechanism for sustained
Finally, acute EtOH activates the GTP-binding protein
H-Ras and inhibits the tyrosine kinase Src to promote
the endocytosis of NR2A-expressing receptors45. This
selective endocytosis results in an increase in the propor-
tion of NMDARs solely expressing the NR2B subunit as
compared to those expressing both the NR2A and NR2B
subunits45. This shift highlights the recruitment of cel-
lular machinery responsible for receptor trafficking in
response to EtOH and may be the initial manifestation of
a more stable shift in subunit ratio observed after chronic
Michael Feyder, et al.
Chronic EtOH and NMDARs
Behavioral tolerance following chronic EtOH treat-
ment (CET) is dependent on repeated NMDAR inhibi-
tion and is blocked following pre-treatment of an NM-
DAR antagonist46. CET results in an up-regulation of
NMDARS as measured by an increase in NMDAR radio-
ligand binding47,48(but see49,50); however, further research
suggests that this up-regulation may be subunit speci?c.
Supporting this hypothesis, CET increases NMDA-
mediated neurotoxicity in neurons found in the cortex51,
the hippocampus52, and the granule cell layer of the cer-
ebellum53. NMDAR-mediated neurotoxicity is thought to
be the result of excessive activation of NR2B-expressing
receptors54suggesting a subunit-speci?c up-regulation of
these receptors. Although the NR1 and NR2A subunits
have been reported to be up-regulated following CET,
NR2B up-regulation has been the most consistently re-
ported and replicated. The subunit is up-regulated in the
cortex55-58, the hippocampus55,59, and the amygdala60,61. In
addition, the NR1 subunit is up-regulated in the ventral
tegmental area (VTA)62. Importantly, glutamatergic in-
puts from the prefrontal cortex, hippocampus and amyg-
dala, along with modulating dopaminergic input from
the VTA, converge and are integrated in the nucleus ac-
cumbens, a region important for reinforced behavior63,64.
Thus, it is hypothesized that NR2B up-regulation follow-
ing CET may underlie the adaptive neurocircuitry driving
persistent EtOH-seeking behavior65.
Supporting this hypothesis, CET alters the electro-
physiological and morphological properties of neurons.
Following CET, ifenprodil occludes the inhibitory effects
of EtOH on excitatory postsynaptic currents in the central
nucleus of the amygdala, an effect that was less in naïve
rats, and suggests an up-regulation of functional NR2B-
expressing receptors66. Similar results were observed
in the lateral/basolateral amygdala61. Structurally, CET
results in an enlargement of dendritic spines as measured
by increased immunoreactivity of the cytoskeletal protein
F-actin and the postsynaptic scaffolding protein PSD-95,
which serves to stabilize synaptic NMDARs and organize
downstream signaling molecules29. Taken together, CET
alters the functional and structural properties of neurons
possibly by up-regulation of NR2B-expressing receptors.
CET-induced up-regulation of NR2B subunits in-
volves a variety of mechanisms. An extracellular physi-
cal interaction between tissue plasminogen activator
(tPA) and the NR2B subunit is required for up-regulation
following CET67. Intracellularly, CET increases DNA
binding and promoter activity of the transcription factor
activator protein 1 (AP-1) at its NR2B-speci?c site68,69.
AP-1 complexes, heterodimers consisting of members
from the Fos, Jun and activating transcription factor (ATF)
protein families70, differ between cortical and cerebellar
granule cells following CET but may involve these vari-
ous protein family68,69.
It is therefore hypothesized that repeated inhibition
of NMDARs following CET results in more structural
homeostatic response involving the up-regulation of
NMDARs. Disruption of this inhibition or in receptor up-
regulation results in abnormal EtOH-related behavior.
Pre-treatment with some, but not all, NMDAR antago-
nists prior to EtOH administration prevents the acquisi-
tion of a conditioned place preference71,72, and has been
reported in mice lacking the NR2A subunit73. Further-
more, mice in which the NR1 subunit was engineered for
a reduced af?nity for glycine, a co-agonist that potenti-
ates NMDAR channel properties, show reduced anxiety-
like behavior and motor incoordination following CET74.
Once NMDAR up-regulation is established, it is
hypothesized that elimination of EtOH results in a hy-
perglutamatergic state that perpetuates EtOH-seeking
behavior75. Global administration76,77or speci?c injection
into the nucleus accumbens78,79of NMDAR antagonists
reduces EtOH self-administration in rodents. Interest-
ingly, administration of an NMDAR antagonist to rats
exposed to stimuli associated with CET reduces EtOH-
seeking behavior when re-presented with EtOH-cues80.
Together, these studies suggest that modi?cation of ex-
cessive glutamatergic transmission may reduce EtOH-
Alcohol dependence and development of pharma-
Clinical research on alcohol dependence supports the
involvement of excessive glutamatergic transmission
mediated by NMDARs. Recovering alcohol-dependent
subjects report less subjective effects after administra-
tion the NMDAR antagonist ketamine, suggestive of a
pre-disposed tolerance due to EtOH-induced NMDAR
upregulation81. Non-dependent subjects with a family
history of alcoholism also showed attenuated responses
to ketamine compared to those with no family history
and suggest that heightened glutamatergic transmission
may be a pre-disposing trait to be exacerbated by chronic
alcohol consumption82. Recovering alcohol-dependent
subjects also have increased levels of glutamate, glycine
and the resulting markers of oxidative stress in their
cerebral spinal fluid83. Finally, the NMDAR antagonist
Ethanol and NMDAneurotransmission
memantine reduces cue-induced craving in recovering
Give the evidence for altered glutamatergic transmis-
sion, preventative and corrective modulation may serve
as a potential pharmacological target in the treatment
of alcohol dependence. Preventative targets include
NMDARs and various downstream signaling molecules
activated following NMDAR inhibition. Prevention of
NMDAR up-regulation by inhibition of transcription
factors, trafficking proteins, synaptic incorporation and
stabilizing scaffolding proteins may prevent excessive
glutamatergic transmission. Once receptor up-regulation
has occurred, targets that restore proper glutamatergic
tone by antagonizing or down-regulating NMDARs, pos-
sibly targeted at NR2B-expressing receptors85, or inhibit-
ing downstream signaling molecules may provide correc-
EtOH inhibits NMDARs within the CNS, with possi-
ble neural functioning and speci?c behavioral responses
mediated by an interaction with the NR2B subunit. As
a result, regionally specific homeostatic responses and
downstream signaling molecules are engaged affecting
channel function, cytoskeletal remodeling and behavior.
Persistent inhibition by EtOH results in up-regulation of
NMDARs, consequential alterations in the functional and
morphological properties of neurons, and activation of
transcription factors to create an excessive glutamatergic
state. Attenuation of this enhanced state reduces EtOH-
seeking behavior and may provide a pharmacological
target for the treatment of alcohol dependence.
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