Alcohol potently inhibits the kainate receptor-dependent excitatory drive of hippocampal interneurons

Ethanol Differentially Affects Excitatory and Inhibitory Synaptic Transmission in Visual Cortex of Wild-type and Adenosine A1R Knock-out Mice

Ethanol is one of the most commonly used and abused substances in the world. While the behavioral effects of ethanol are well characterized, mechanisms of its action on neurons and synapses remain elusive. Prior research suggested that ethanol could affect neurons by interfering with metabolism of biologically active molecules, such as adenosine. Here, we explored the involvement of adenosine A1 receptors (A1R) in mediating ethanol's effects on synaptic transmission to layer 2/3 pyramidal neurons of visual cortex using wild type (WT) and A1R knock-out (KO) mice. Ethanol differentially affected excitatory and inhibitory transmission in WT and KO mice. In slices from WT mice ethanol had heterogeneous effects on excitatory transmission (facilitation, suppression or no change), with no net change. Ethanol's effects remained heterogeneous during acute blockade of A1Rs with a selective antagonist DPCPX. However, in A1RKO mice ethanol consistently suppressed excitatory transmission, with no cases of enhancement observed. Inhibitory transmission was suppressed by ethanol in both WT and A1RKO mice. At both excitatory and inhibitory synapses, changes of response amplitude correlated with changes of paired-pulse ratio, suggesting involvement of presynaptic mechanisms. We conclude that A1Rs are not involved in mediating effects of ethanol on synaptic transmission in mouse visual cortex. However, A1Rs are necessary for development of mechanisms mediating facilitation at some excitatory synapses. Our results add evidence for the diversity of ethanol's effects and mechanisms of action on synaptic transmission in different brain structures, and even in the same brain area (visual cortex) in different species, rats vs mice.

Acute alcohol induces greater dose-dependent increase in the lateral cortical network functional connectivity in adult than adolescent rats

Alcohol misuse and, particularly adolescent drinking, is a major public health concern. While evidence suggests that adolescent alcohol use affects frontal brain regions that are important for cognitive control over behavior little is known about how acute alcohol exposure alters large-scale brain networks and how sex and age may moderate such effects. Here, we employ a recently developed functional magnetic resonance imaging (fMRI) protocol to acquire rat brain functional connectivity data and use an established analytical pipeline to examine the effect of sex, age, and alcohol dose on connectivity within and between three major rodent brain networks: defaul mode, salience, and lateral cortical network. We identify the intra- and inter-network connectivity differences and establish moderation models to reveal significant influences of age on acute alcohol-induced lateral cortical network connectivity. Through this work, we make brain-wide isotropic fMRI data with acute alcohol challenge publicly available, with the hope to facilitate future discovery of brain regions/circuits that are causally relevant to the impact of acute alcohol use.

Allosteric Modulators of Metabotropic Glutamate Receptors as Novel Therapeutics for Neuropsychiatric Disease

Metabotropic glutamate (mGlu) receptors, a family of G-protein-coupled receptors, have been identified as novel therapeutic targets based on extensive research supporting their diverse contributions to cell signaling and physiology throughout the nervous system and important roles in regulating complex behaviors, such as cognition, reward, and movement. Thus, targeting mGlu receptors may be a promising strategy for the treatment of several brain disorders. Ongoing advances in the discovery of subtype-selective allosteric modulators for mGlu receptors has provided an unprecedented opportunity for highly specific modulation of signaling by individual mGlu receptor subtypes in the brain by targeting sites distinct from orthosteric or endogenous ligand binding sites on mGlu receptors. These pharmacological agents provide the unparalleled opportunity to selectively regulate neuronal excitability, synaptic transmission, and subsequent behavioral output pertinent to many brain disorders. Here, we review preclinical and clinical evidence supporting the utility of mGlu receptor allosteric modulators as novel therapeutic approaches to treat neuropsychiatric diseases, such as schizophrenia, substance use disorders, and stress-related disorders. SIGNIFICANCE STATEMENT: Allosteric modulation of metabotropic glutamate (mGlu) receptors represents a promising therapeutic strategy to normalize dysregulated cellular physiology associated with neuropsychiatric disease. This review summarizes preclinical and clinical studies using mGlu receptor allosteric modulators as experimental tools and potential therapeutic approaches for the treatment of neuropsychiatric diseases, including schizophrenia, stress, and substance use disorders.

Patterns of functional connectivity alterations induced by alcohol reflect somatostatin interneuron expression in the human cerebral cortex

Acute alcohol administration affects functional connectivity, yet the underlying mechanism is unknown. Previous work suggested that a moderate dose of alcohol reduces the activity of gamma-aminobutyric acidergic (GABAergic) interneurons, thereby leading to a state of pyramidal disinhibition and hyperexcitability. The present study aims to relate alcohol-induced changes in functional connectivity to regional genetic markers of GABAergic interneurons. Healthy young adults (N = 15, 5 males) underwent resting state functional MRI scanning prior to alcohol administration, immediately and 90 min after alcohol administration. Functional connectivity density mapping was performed to quantify alcohol-induced changes in resting brain activity between conditions. Patterns of differences between conditions were related to regional genetic markers that express the primary GABAergic cortical interneuron subtypes (parvalbumin, somatostatin, and 5-hydroxytryptamine receptor 3A) obtained from the Allen Human Brain Atlas. Acute alcohol administration increased local functional connectivity density within the visual cortex, sensorimotor cortex, thalamus, striatum, and cerebellum. Patterns of alcohol-induced changes in local functional connectivity density inversely correlated with somatostatin cortical gene expression. These findings suggest that somatostatin-expressing interneurons modulate alcohol-induced changes in functional connectivity in healthy individuals.

Low-dose alcohol: Interoceptive and molecular effects and the role of dentate gyrus in rats

Alcohol abuse and dependence are world-wide health problems. Most research on alcohol use focuses on the consequences of moderate to high levels of alcohol. However, even at low concentrations, alcohol is capable of producing effects in the brain that can ultimately affect behavior. The current studies seek to understand the effects of low-dose alcohol (blood alcohol levels of ≤10mM). To do so, these experiments utilize a combination of behavioral and molecular techniques to (1) assess the ability of the interoceptive effects of a low dose of alcohol to gain control over goal-tracking behavior in a Pavlovian discrimination task, (2) determine brain regional differences in cellular activity via expression of immediate early genes (IEGs), and (3) assess the role of the dentate gyrus in modulating sensitivity to the interoceptive effects of a low dose of alcohol. Here, we show that intragastric administration of a dose of 0.8 g/kg alcohol produces blood alcohol levels ≤10mM in both male and female Long-Evans rats and can readily be trained as a Pavlovian interoceptive drug cue. In rats trained on this procedure, this dose of alcohol also modulates expression of the IEGs c-Fos and Arc in brain regions known to modulate expression of alcohol interoceptive effects. Finally, pharmacological inactivation of the dentate gyrus with GABA agonists baclofen and muscimol disrupted the ability of a low dose of alcohol to serve as an interoceptive cue. Together, these findings demonstrate behavioral and molecular consequences of low-dose alcohol.

Neonatal ethanol exposure triggers apoptosis in the murine retrosplenial cortex: Role of inhibition of NMDA receptor-driven action potential firing

Exposure to ethanol during the last trimester equivalent of human pregnancy causes apoptotic neurodegeneration in the developing brain, an effect that is thought to be mediated, in part, by inhibition of NMDA receptors. However, NMDA receptors can rapidly adapt to the acute effects of ethanol and are ethanol resistant in some populations of developing neurons. Here, we characterized the effect of ethanol on NMDA and non-NMDA receptor-mediated synaptic transmission in the retrosplenial cortex (RSC), a brain region involved in the integration of different modalities of spatial information that is among the most sensitive regions to ethanol-induced neurodegeneration. A single 4-h exposure to ethanol vapor of 7-day-old transgenic mice that express the Venus fluorescent protein in interneurons triggered extensive apoptosis in the RSC. Slice electrophysiological recordings showed that bath-applied ethanol inhibits NMDA and non-NMDA receptor excitatory postsynaptic currents (EPSCs) in pyramidal neurons and interneurons; however, we found no evidence of acute tolerance development to this effect after the 4-h in-vivo ethanol vapor exposure. Acute bath application of ethanol reduced action potential firing evoked by synaptic stimulation to a greater extent in pyramidal neurons than interneurons. Submaximal inhibition of NMDA EPSCs, but not non-NMDA EPSCs, mimicked the acute effect of ethanol on synaptically-evoked action potential firing. These findings indicate that partial inhibition of NMDA receptors by ethanol has sizable effects on the excitability of glutamatergic and GABAergic neurons in the developing RSC, and suggest that positive allosteric modulators of these receptors could ameliorate ethanol intoxication-induced neurodegeneration during late stages of fetal development.

Role of glutamatergic system and mesocorticolimbic circuits in alcohol dependence

Emerging evidence demonstrates that alcohol dependence is associated with dysregulation of several neurotransmitters. Alterations in dopamine, glutamate and gamma-aminobutyric acid release are linked to chronic alcohol exposure. The effects of alcohol on the glutamatergic system in the mesocorticolimbic areas have been investigated extensively. Several studies have demonstrated dysregulation in the glutamatergic systems in animal models exposed to alcohol. Alcohol exposure can lead to an increase in extracellular glutamate concentrations in mesocorticolimbic brain regions. In addition, alcohol exposure affects the expression and functions of several glutamate receptors and glutamate transporters in these brain regions. In this review, we discussed the effects of alcohol exposure on glutamate receptors, glutamate transporters and glutamate homeostasis in each area of the mesocorticolimbic system. In addition, we discussed the genetic aspect of alcohol associated with glutamate and reward circuitry. We also discussed the potential therapeutic role of glutamate receptors and glutamate transporters in each brain region for the treatment of alcohol dependence. Finally, we provided some limitations on targeting the glutamatergic system for potential therapeutic options for the treatment alcohol use disorders.

Epigenetic Regulation of Glutamic Acid Decarboxylase 67 in a Hippocampal Circuit

GABAergic dysfunction in hippocampus, a key feature of schizophrenia (SZ), may contribute to cognitive impairment in this disorder. In stratum oriens (SO) of sector CA3/2 of the human hippocampus, a network of genes involved in the regulation of glutamic acid decarboxylase GAD67 has been identified. Several of the genes in this network including epigenetic factors histone deacetylase 1 (HDAC1) and death-associated protein 6 (DAXX), the GABAergic enzyme GAD65 as well as the kainate receptor (KAR) subunits GluR6 and 7 show significant changes in expression in this area in SZ. We have tested whether HDAC1 and DAXX regulate GAD67, GAD65, or GluR in the intact rodent hippocampus. Stereotaxic injections of lentiviral vectors bearing shRNAi sequences for HDAC1 and DAXX were delivered into the SO of CA3/2, followed by laser microdissection of individual transduced GABA neurons. Quantitative PCR (QPCR) analyses demonstrated that inhibition of HDAC1 and DAXX increased expression of GAD67, GAD65, and GluR6 mRNA. Inhibition of DAXX, but not HDAC1 resulted in a significant increase in GluR7 mRNA. Our data support the hypothesis that HDAC1 and DAXX play a central role in coordinating the expression of genes in the GAD67 regulatory pathway in the SO of CA3/2.

Effects of acute alcohol on excitability in the CNS

Alcohol has many effects on brain function and hence on human behavior, ranging from anxiolytic and mild disinhibitory effects, sedation and motor incoordination, amnesia, emesis, hypnosis and eventually unconsciousness. In recent years a variety of studies have shown that acute and chronic exposure to alcohol can modulate ion channels that regulate excitability. Modulation of intrinsic excitability provides another way in which alcohol can influence neuronal network activity, in addition to its actions on synaptic inputs. In this review, we review "low dose" effects [between 2 and 20 mM EtOH], and "medium dose"; effects [between 20 and 50 mM], by considering in turn each of the many networks and brain regions affected by alcohol, and thereby attempt to integrate in vitro physiological studies in specific brain regions (e.g. amygdala, ventral tegmental area, prefrontal cortex, thalamus, cerebellum etc.) within the context of alcohol's behavioral actions in vivo (e.g. anxiolysis, euphoria, sedation, motor incoordination). This article is part of the Special Issue entitled "Alcoholism".

Titrating Tipsy Targets: The Neurobiology of Low-Dose Alcohol

Limited attention has been given to our understanding of how the brain responds to low-dose alcohol (ethanol) and what molecular and cellular targets mediate these effects. Even at concentrations lower than 10mM (0.046 g% blood alcohol concentration, BAC), below the legal driving limit in the USA (BAC 0.08 g%), alcohol impacts brain function and behavior. Understanding what molecular and cellular targets mediate the initial effects of alcohol and subsequent neuroplasticity could provide a better understanding of vulnerability or resilience to developing alcohol use disorders. We review here what is known about the neurobiology of low-dose alcohol, provide insights into potential molecular targets, and discuss future directions and challenges in further defining targets of low-dose alcohol at the molecular, cellular, and circuitry levels.

Ethanol alters the expression of ion channel genes in Daphnia pulex

BACKGROUND

Heavy drinking can increase heart rate and blood glucose, induce hypoxic tolerance, impair brain cognitive functions, and alter gene expressions. These phenomena may occur even in response to small dose of ethanol exposure or during its withdrawal.

OBJECTIVES

To evaluate whether persistent low concentrations of ethanol exposure affect organism function and the gene expressions of ion channels.

METHODS

Daphnids were randomized to receive placebo 300 min, 2 mM ethanol 300 min, or 2 mM ethanol 240 min and then placebo 60 min. Heart rate, glucose levels, phototactic behavior, and hypoxic tolerance were recorded during experiment. At the end of the study, changes in the mRNA levels of ion channel genes were assessed in response to exposure to ethanol using quantitative polymerase chain reaction (PCR) techniques.

RESULTS

Heart rate was reversibly increased by ethanol withdrawal and returned to basal levels upon re-exposure to ethanol. Fifteen of 120 ion channel transcripts were affected by persistent ethanol exposure. Neither ethanol withdrawal nor persistent exposures showed an effect on blood glucose, phototactic behavior, or hypoxic tolerance.

CONCLUSIONS

Small doses of ethanol can increase heart rate and alter gene expression of multiple ion channels in Daphnia pulex. Affected ion channel genes may assist in understanding the mechanism of ethanol adaptation and tolerance.

Glutamatergic transmission in drug reward: implications for drug addiction

Individuals addicted to drugs of abuse such as alcohol, nicotine, cocaine, and heroin are a significant burden on healthcare systems all over the world. The positive reinforcing (rewarding) effects of the above mentioned drugs play a major role in the initiation and maintenance of the drug-taking habit. Thus, understanding the neurochemical mechanisms underlying the reinforcing effects of drugs of abuse is critical to reducing the burden of drug addiction in society. Over the last two decades, there has been an increasing focus on the role of the excitatory neurotransmitter glutamate in drug addiction. In this review, pharmacological and genetic evidence supporting the role of glutamate in mediating the rewarding effects of the above described drugs of abuse will be discussed. Further, the review will discuss the role of glutamate transmission in two complex heterogeneous brain regions, namely the nucleus accumbens (NAcc) and the ventral tegmental area (VTA), which mediate the rewarding effects of drugs of abuse. In addition, several medications approved by the Food and Drug Administration that act by blocking glutamate transmission will be discussed in the context of drug reward. Finally, this review will discuss future studies needed to address currently unanswered gaps in knowledge, which will further elucidate the role of glutamate in the rewarding effects of drugs of abuse.

Chronic exposure to alcohol alters network activity and morphology of cultured hippocampal neurons

The effects of chronic exposure to moderate concentrations of ethanol were studied in cultured hippocampal neurons. Network activity, assessed by imaging of [Ca(2+)]i variations, was markedly suppressed following 5 days of exposure to 0.25-1% ethanol. The reduced activity was sustained following extensive washout of ethanol, but the activity recovered by blockade of inhibition with bicuculline. This reduction of network activity was associated with a reduction in rates of mEPSCs, but not in a change in inhibitory synaptic activity. Chronic exposure to ethanol caused a significant reduction in the density of mature dendritic spines, without an effect on dendritic length or arborization. These results indicate that chronic exposure to ethanol causes a reduction in excitatory network drive in hippocampal neurons adding another dimension to the chronic effects of alcohol abuse.

Expression of specific ionotropic glutamate and GABA-A receptor subunits is decreased in central amygdala of alcoholics

The central amygdala (CeA) has a role for mediating fear and anxiety responses. It is also involved in emotional imbalance caused by alcohol abuse and dependence and in regulating relapse to alcohol abuse. Growing evidences suggest that excitatory glutamatergic and inhibitory γ-aminobutyric acid-ergic (GABAergic) transmissions in the CeA are affected by chronic alcohol exposure. Human post-mortem CeA samples from male alcoholics (n = 9) and matched controls (n = 9) were assayed for the expression level of ionotropic glutamate and GABA-A receptors subunit mRNAs using quantitative real-time reverse transcription-PCR (RT-qPCR). Our data revealed that out of the 16 ionotropic glutamate receptor subunits, mRNAs encoding two AMPA [2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid] receptor subunits GluA1 and GluA4; one kainate receptor subunit GluK2; one NMDA (N-methyl-D-aspartate) receptor subunit GluN2D and one delta receptor subunit GluD2 were significantly decreased in the CeA of alcoholics. In contrast, of the 19 GABA-A receptor subunits, only the mRNA encoding the α2 subunit was significantly down-regulated in the CeA of the alcoholics as compared with control subjects. Our findings imply that the down-regulation of specific ionotropic glutamate and GABA-A receptor subunits in the CeA of alcoholics may represent one of the molecular substrates underlying the new balance between excitatory and inhibitory neurotransmission in alcohol dependence.

The mammalian circadian clock in the suprachiasmatic nucleus exhibits rapid tolerance to ethanol in vivo and in vitro

BACKGROUND

Ethanol (EtOH) triggers cellular adaptations that induce tolerance in many brain areas, including the suprachiasmatic nucleus (SCN), the site of the master circadian clock. EtOH inhibits light-induced phase shifts in the SCN in vivo and glutamate-induced phase shifts in vitro. The in vitro phase shifts develop acute tolerance to EtOH, occurring within minutes of initial exposure, while the in vivo phase shifts exhibit no evidence of chronic tolerance. An intermediate form, rapid tolerance, is not well studied but may predict subsequent chronic tolerance. Here, we investigated rapid tolerance in the SCN clock.

METHODS

Adult C57BL/6 mice were provided 15% EtOH or water for one 12-hour lights-off period. For in vitro experiments, SCN-containing brain slices were prepared in the morning and treated for 10 minutes with glutamate +/- EtOH the following night. Single-cell neuronal firing rates were recorded extracellularly during the subsequent day to determine SCN clock phase. For in vivo experiments, mice receiving EtOH 24 hours previously were exposed to a 30-minute light pulse immediately preceded by intraperitoneal saline or 2 g/kg EtOH injection. Mice were then placed in constant darkness and their phase-shifting responses measured.

RESULTS

In vitro, the SCN clock from EtOH-exposed mice exhibited rapid tolerance, with a 10-fold increase in EtOH needed to inhibit glutamate-induced phase shifts. Co-application of brain-derived neurotrophic factor prevented EtOH inhibition, consistent with experiments using EtOH-naïve mice. Rapid tolerance lasts 48 to 96 hours, depending on whether assessing in vitro phase advances or phase delays. Similarly, in vivo, prior EtOH consumption prevented EtOH's acute blockade of photic phase delays. Finally, immunoblot experiments showed no changes in SCN glutamate receptor subunit (NR2B) expression or phosphorylation in response to rapid tolerance induction.

CONCLUSIONS

The SCN circadian clock develops rapid tolerance to EtOH as assessed both in vivo and in vitro, and the tolerance lasts for several days. These data demonstrate the utility of the circadian system as a model for investigating cellular mechanisms through which EtOH acts in the brain.

Acute and chronic effects of ethanol on learning-related synaptic plasticity

Alcoholism is associated with acute and long-term cognitive dysfunction including memory impairment, resulting in substantial disability and cost to society. Thus, understanding how ethanol impairs cognition is essential for developing treatment strategies to dampen its adverse impact. Memory processing is thought to involve persistent, use-dependent changes in synaptic transmission, and ethanol alters the activity of multiple signaling molecules involved in synaptic processing, including modulation of the glutamate and gamma-aminobutyric acid (GABA) transmitter systems that mediate most fast excitatory and inhibitory transmission in the brain. Effects on glutamate and GABA receptors contribute to ethanol-induced changes in long-term potentiation (LTP) and long-term depression (LTD), forms of synaptic plasticity thought to underlie memory acquisition. In this paper, we review the effects of ethanol on learning-related forms of synaptic plasticity with emphasis on changes observed in the hippocampus, a brain region that is critical for encoding contextual and episodic memories. We also include studies in other brain regions as they pertain to altered cognitive and mental function. Comparison of effects in the hippocampus to other brain regions is instructive for understanding the complexities of ethanol's acute and long-term pharmacological consequences.

Ethanol affects network activity in cultured rat hippocampus: mediation by potassium channels

The effects of ethanol on neuronal network activity were studied in dissociated cultures of rat hippocampus. Exposure to low (0.25–0.5%) ethanol concentrations caused an increase in synchronized network spikes, and a decrease in the duration of individual spikes. Ethanol also caused an increase in rate of miniature spontaneous excitatory postsynaptic currents. Higher concentrations of ethanol eliminated network spikes. These effects were reversible upon wash. The effects of the high, but not the low ethanol were blocked by the GABA antagonist bicuculline. The enhancing action of low ethanol was blocked by apamin, an SK potassium channel antagonist, and mimicked by 1-EBIO, an SK channel opener. It is proposed that in cultured hippocampal networks low concentration of ethanol is associated with SK channel activity, rather than the GABAergic receptor.

Neural control of the upper airway: integrative physiological mechanisms and relevance for sleep disordered breathing

The various neural mechanisms affecting the control of the upper airway muscles are discussed in this review, with particular emphasis on structure-function relationships and integrative physiological motor-control processes. Particular foci of attention include the respiratory function of the upper airway muscles, and the various reflex mechanisms underlying their control, specifically the reflex responses to changes in airway pressure, reflexes from pulmonary receptors, chemoreceptor and baroreceptor reflexes, and postural effects on upper airway motor control. This article also addresses the determinants of upper airway collapsibility and the influence of neural drive to the upper airway muscles, and the influence of common drugs such as ethanol, sedative hypnotics, and opioids on upper airway motor control. In addition to an examination of these basic physiological mechanisms, consideration is given throughout this review as to how these mechanisms relate to integrative function in the intact normal upper airway in wakefulness and sleep, and how they may be involved in the pathogenesis of clinical problems such obstructive sleep apnea hypopnea.

Glutamatergic targets for new alcohol medications

RATIONALE

An increasingly compelling literature points to a major role for the glutamate system in mediating the effects of alcohol on behavior and the pathophysiology of alcoholism. Preclinical studies indicate that glutamate signaling mediates certain aspects of ethanol's intoxicating and rewarding effects, and undergoes adaptations following chronic alcohol exposure that may contribute to the withdrawal, craving and compulsive drug-seeking that drive alcohol abuse and alcoholism.

OBJECTIVES

We discuss the potential for targeting the glutamate system as a novel pharmacotherapeutic approach to treating alcohol use disorders, focusing on five major components of the glutamate system: the N-methyl-D-aspartate (NMDA) receptor and specific NMDA subunits, the glycineB site on the NMDA receptors (NMDAR), L-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid ionotropic (AMPA) and kainate (KAR) receptors, metabotropic receptors (mGluR), and glutamate transporters.

RESULTS

Chronic alcohol abuse produces a hyperglutamatergic state, characterized by elevated extracellular glutamate and altered glutamate receptors and transporters. Pharmacologically manipulating glutamatergic neurotransmission alters alcohol-related behaviors including intoxication, withdrawal, and alcohol-seeking, in rodents and human subjects. Blocking NMDA and AMPA receptors reduces alcohol consumption in rodents, but side-effects may limit this as a therapeutic approach. Selectively targeting NMDA and AMPA receptor subunits (e.g., GluN2B, GluA3), or the NMDAR glycineB site offers an alternative approach. Blocking mGluR5 potently affects various alcohol-related behaviors in rodents, and mGluR2/3 agonism also suppresses alcohol consumption. Finally, glutamate transporter upregulation may mitigate behavioral and neurotoxic sequelae of excess glutamate caused by alcohol.

CONCLUSIONS

Despite the many challenges that remain, targeting the glutamate system offers genuine promise for developing new treatments for alcoholism.

Alcohol and NMDA receptor: current research and future direction

The brain is one of the major targets of alcohol actions. Most of the excitatory synaptic transmission in the central nervous system is mediated by N-methyl-D-aspartate (NMDA) receptors. However, one of the most devastating effects of alcohol leads to brain shrinkage, loss of nerve cells at specific regions through a mechanism involving excitotoxicity, oxidative stress. Earlier studies have indicated that chronic exposure to ethanol both in vivo and in vitro, increases NR1 and NR2B gene expression and their polypeptide levels. The effect of alcohol and molecular changes on the regulatory process, which modulates NMDAR functions including factors altering transcription, translation, post-translational modifications, and protein expression, as well as those influencing their interactions with different regulatory proteins (downstream effectors) are incessantly increasing at the cellular level. Further, I discuss the various genetically altered mice approaches that have been used to study NMDA receptor subunits and their functional implication. In a recent countable review, epigenetic dimension (i.e., histone modification-induced chromatin remodeling and DNA methylation, in the process of alcohol related neuroadaptation) is one of the key molecular mechanisms in alcohol mediated NMDAR alteration. Here, I provide a recount on what has already been achieved, current trends and how the future research/studies of the NMDA receptor might lead to even greater engagement with many possible new insights into the neurobiology and treatment of alcoholism.

Acute effects of ethanol on glutamate receptors

Several studies have revealed that acute ethanol inhibits the function of glutamate receptors. Glutamate receptor-mediated synaptic plasticity, such as N-methyl-D-aspartate-dependent long-term potentiation, is also inhibited by ethanol. However, the inhibition seems to be restricted to certain brain areas such as the hippocampus, amygdala and striatum. Ethanol inhibition of glutamate receptors generally requires relatively high concentrations and may therefore explain consequences of severe ethanol intoxication such as impairment of motor performance and memory. Effects of ethanol on glutamate system of developing nervous system may have a role in causing foetal alcohol syndrome. Newly found regulatory proteins of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid AMPA receptors seem to affect ethanol inhibition thus opening new lines of research.

Opposite effects of acute ethanol exposure on GAP-43 and BDNF expression in the hippocampus versus the cerebellum of juvenile rats

The adolescent brain is particularly vulnerable to the effects of alcohol, with intoxications at this developmental age often producing long-lasting effects. The present study addresses the effects of a single acute ethanol exposure on growth-associated protein-43 (GAP-43) and brain-derived neurotrophic factor (BDNF) gene expression in neurons in the cerebellum and hippocampus of adolescent rats. Male postnatal day 23 (P23) Sprague-Dawley rats were exposed to ethanol vapors for 2h and after a recovery period of 2h, the cerebellum and hippocampus were harvested and samples were taken for blood alcohol concentration (BAC) determinations. We found that this exposure resulted in a mean BAC of 174 mg/dL, which resembles levels in human adolescents after binge drinking. Analyses of total RNA and protein by quantitative reverse transcription PCR and western blotting, respectively, revealed that this single ethanol exposure significantly decreased the levels of GAP-43 mRNA and protein in the cerebellum but increased the levels of mRNA and protein in the hippocampus. BDNF mRNA and protein levels were also increased in the hippocampus but not in the cerebellum of these animals. In situ hybridizations revealed that GAP-43 and BDNF mRNA levels were primarily increased by alcohol exposure in hippocampal dentate granule cells and CA3 neurons. Overall, the reported alterations in the expression of the plasticity-associated genes GAP-43 and BDNF in juvenile rats are consistent with the known deleterious effects of binge drinking on motor coordination and cognitive function.

Alcohol induces synaptotagmin 1 expression in neurons via activation of heat shock factor 1

Many synapses within the central nervous system are sensitive to ethanol. Although alcohol is known to affect the probability of neurotransmitter release in specific brain regions, the effects of alcohol on the underlying synaptic vesicle fusion machinery have been little studied. To identify a potential pathway by which ethanol can regulate neurotransmitter release, we investigated the effects of acute alcohol exposure (1-24 h) on the expression of the gene encoding synaptotagmin 1 (Syt1), a synaptic protein that binds calcium to directly trigger vesicle fusion. Syt1 was identified in a microarray screen as a gene that may be sensitive to alcohol and heat shock. We found that Syt1 mRNA and protein expression are rapidly and robustly up-regulated by ethanol in mouse cortical neurons, and that the distribution of Syt1 protein along neuronal processes is also altered. Syt1 mRNA up-regulation is dependent on the activation of the transcription factor heat shock factor 1 (HSF1). The transfection of a constitutively active Hsf1 construct into neurons stimulates Syt1 transcription, while transfection of Hsf1 small interfering RNA (siRNA) or a constitutively inactive Hsf1 construct into neurons attenuates the induction of Syt1 by ethanol. This suggests that the activation of HSF1 can induce Syt1 expression and that this may be a mechanism by which alcohol regulates neurotransmitter release during brief exposures. Further analysis revealed that a subset of the genes encoding the core synaptic vesicle fusion (soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein receptor; SNARE) proteins share this property of induction by ethanol, suggesting that alcohol may trigger a specific coordinated adaptation in synaptic function. This molecular mechanism could explain some of the changes in synaptic function that occur following alcohol administration and may be an important step in the process of neuronal adaptation to alcohol.

Ethanol affects striatal interneurons directly and projection neurons through a reduction in cholinergic tone

The acute effects of ethanol on the neurons of the striatum, a basal ganglia nucleus crucially involved in motor control and action selection, were investigated using whole-cell recordings. An intoxicating concentration of ethanol (50 mM) produced inhibitory effects on striatal large aspiny cholinergic interneurons (LAIs) and low-threshold spike interneurons (LTSIs). These effects persisted in the presence of tetrodotoxin and were because of an increase in potassium currents, including those responsible for medium and slow afterhyperpolarizations. In contrast, fast-spiking interneurons (FSIs) were directly excited by ethanol, which depolarized these neurons through the suppression of potassium currents. Medium spiny neurons (MSNs) became hyperpolarized in the presence of ethanol, but this effect did not persist in the presence of tetrodotoxin and was mimicked and occluded by application of the M1 muscarinic receptor antagonist telenzepine. Ethanol effects on MSNs were also abolished by 100 μM barium. This showed that the hyperpolarizations observed in MSNs were because of decreased tonic activation of M1 muscarinic receptors, resulting in an increase in Kir2 conductances. Evoked GABAergic responses of MSNs were reversibly decreased by ethanol with no change in paired-pulse ratio. Furthermore, ethanol impaired the ability of thalamostriatal inputs to inhibit a subsequent corticostriatal glutamatergic response in MSNs. These results offer the first comprehensive description of the highly cell type-specific effects of ethanol on striatal neurons and provide a cellular basis for the interpretation of ethanol influence on a brain area crucially involved in the motor and decisional impairment caused by this drug.

Voluntary Ethanol Consumption Induced by Social Isolation Reverses the Increase of α(4)/δ GABA(A) Receptor Gene Expression and Function in the Hippocampus of C57BL/6J Mice

Post-weaning social isolation (SI) is a model of prolonged mild stress characterized by behavioral and neurochemical alterations. We used SI in C57BL/6J mice to investigate the effects of ethanol (EtOH) in the free-choice drinking paradigm on gene expression and function of γ-aminobutyric acid type A receptors (GABA_ARs) and the role of neuroactive steroids in the actions of EtOH in the hippocampus. SI stress induced a marked reduction in hippocampal 3α-hydroxy-5α-pregnan-20-one (3α,5α-TH PROG) and was associated with molecular and functional changes of the GABA_AR. The gene expression of the α₄ and δ subunits was increased in the hippocampus of SI C57BL/6J mice; the expression of the γ₂ subunit was decreased whereas that of the α₁ did not change. Patch-clamp recordings in dentate gyrus (DG) granule cells obtained from SI C57BL/6J mice revealed a greater enhancement of tonic currents induced by α-(4,5,6,7-tetrahydroisoxazolo[5,4-c] pyridin-3-ol (THIP) compared to that in control C57BL/6J mice. These neurochemical, molecular and functional changes observed in SI C57BL/6J mice were associated with an increased EtOH intake and EtOH preference. Nevertheless, the increase in EtOH consumption did not restore the reduction in hippocampal 3α,5α-TH PROG induced by SI. EtOH self-administration blocked the changes in gene expression of the α₄ subunit but not those of the δ and γ₂ subunits induced by SI. In addition, EtOH self-administration did not block the SI-induced changes in GABA_AR-mediated tonic inhibition in hippocampal granule cells but increased the frequency of basal GABAergic sIPSCs in DG granule cells. We conclude that self-administration of EtOH selectively abolishes the increase of α₄ subunit but not other neurochemical, molecular, and functional modifications induced by SI prolonged mild stress.

Alternative splicing of AMPA subunits in prefrontal cortical fields of cynomolgus monkeys following chronic ethanol self-administration

Functional impairment of the orbital and medial prefrontal cortex underlies deficits in executive control that characterize addictive disorders, including alcohol addiction. Previous studies indicate that alcohol alters glutamate neurotransmission and one substrate of these effects may be through the reconfiguration of the subunits constituting ionotropic glutamate receptor (iGluR) complexes. Glutamatergic transmission is integral to cortico-cortical and cortico-subcortical communication and alcohol-induced changes in the abundance of the receptor subunits and/or their splice variants may result in critical functional impairments of prefrontal cortex in alcohol dependence. To this end, the effects of chronic ethanol self-administration on glutamate receptor ionotropic AMPA (GRIA) subunit variant and kainate (GRIK) subunit mRNA expression were studied in the orbitofrontal cortex (OFC), dorsolateral prefrontal cortex (DLPFC), and anterior cingulate cortex (ACC) of male cynomolgus monkeys. In DLPFC, total AMPA splice variant expression and total kainate receptor subunit expression were significantly decreased in alcohol drinking monkeys. Expression levels of GRIA3 flip and flop and GRIA4 flop mRNAs in this region were positively correlated with daily ethanol intake and blood ethanol concentrations (BEC) averaged over the 6 months prior to necropsy. In OFC, AMPA subunit splice variant expression was reduced in the alcohol treated group. GRIA2 flop mRNA levels in this region were positively correlated with daily ethanol intake and BEC averaged over the 6 months prior to necropsy. Results from these studies provide further evidence of transcriptional regulation of iGluR subunits in the primate brain following chronic alcohol self-administration. Additional studies examining the cellular localization of such effects in the framework of primate prefrontal cortical circuitry are warranted.

Regulation of cell cycle and DNA repair in post-mitotic GABA neurons in psychotic disorders

Disturbances of cell cycle regulation and DNA repair in post-mitotic neurons have been implicated in degenerative and malignant diseases of the human brain. Recent work is now suggesting that abnormal regulation of these functions in GABA cells of the adult hippocampus may also play a role in two neuropsychiatric disorders. In schizophrenia and bipolar disorder, a network of genes involved in the regulation of GAD₆₇, a marker for the functional differentiation of GABA cells, show pronounced changes in expression and include kainate receptor subunits, TGFβ and Wnt signaling pathways, epigenetic factors and transcription factors. One of these genes, cyclin D2, is involved in the regulation of cell cycle and DNA repair and appears to be a pivotal element in linking GAD₆₇ expression with these functional clusters of genes. Dysfunction of post-mitotic GABAergic neurons in the adult hippocampus of patients with psychotic disorders is associated with changes in the expression of genes that are involved in the maintenance of functional and genomic integrity of GABA cells. The nature of these changes is quite different in schizophrenia and bipolar disorder, suggesting that a common cell phenotype (in this case, decreased GAD₆₇ expression) may involve two fundamentally different molecular endophenotypes and reflect unique susceptibility genes involved in the respective disorders. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Differential sensitivity of hippocampal interneurons to ethanol in adolescent and adult rats

Ethanol (EtOH) promotes GABAergic synaptic transmission in the central nervous system. We have shown that EtOH enhances the frequency of GABA(A) receptor-mediated spontaneous inhibitory postsynaptic currents less powerfully in hippocampal CA1 pyramidal neurons from adolescent animals compared with those from adults. However, we have also shown that EtOH promotes the firing of hippocampal interneurons, located in stratum lacunosum moleculare (SLM), from adolescent animals more potently than in those from adults. Thus the latter finding would seem to be inconsistent with the former. To understand this apparent inconsistency, we have now assessed the effects of EtOH on a different subpopulation of hippocampal interneurons, those with somata located in the stratum oriens (SO). We found that EtOH-induced enhancement of the frequency of spontaneous action potentials (sAPs) was less in interneurons from adolescent rats compared with those from adults. In addition, EtOH-induced reduction of the afterhyperpolarization decay time constant (τ(slow)) was less pronounced in interneurons from adolescent rats, as was the EtOH-induced increase in the amplitude of the hyperpolarization-activated cation current, I(h). The effect of EtOH on sAP firing frequency was blocked by application of the I(h) antagonist 4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride (ZD7288). These results indicate that although EtOH promotes the firing of hippocampal interneurons, through promotion of I(h), the developmental expression of this effect differs between interneurons with somata located in the SO and SLM.

The neurobiology, clinical efficacy and safety of acamprosate in the treatment of alcohol dependence

IMPORTANCE TO THE FIELD

Acamprosate, marketed under the brand name Campral, (Forest Pharmaceuticals, Inc., Saint Louis, MO, USA; Merck Sante s.a.s., Lyon, France) is an orally administered drug approved in the US and throughout much of the world for treating alcohol dependence. Its safety and efficacy have been demonstrated in a number of clinical trials worldwide and as with all pharmacotherapies for alcoholism, it is used in conjunction with psychosocial interventions.

AREAS COVERED IN THIS REVIEW

This article reviews the mechanism of action, clinical efficacy and safety of acamprosate in Phase I, II and III randomized controlled trials involving healthy and alcohol-dependent populations using published reports from 1984 to 2009.

WHAT THE READER WILL GAIN

This review provides an update of the mechanism of action and the safety and efficacy profile of acamprosate.

TAKE HOME MESSAGE

Acamprosate appears to act centrally to restore the normal activity of glutamatergic neurotransmission altered by chronic alcohol exposure. Acamprosate's excellent safety profile along with several pharmacokinetic and pharmacodynamic characteristics make it well suited for treating a broad population of alcohol-dependent patients.

Ethanol acutely inhibits ionotropic glutamate receptor-mediated responses and long-term potentiation in the developing CA1 hippocampus

BACKGROUND

Developmental ethanol (EtOH) exposure damages the hippocampus, causing long-lasting alterations in learning and memory. Alterations in glutamatergic synaptic transmission and plasticity may play a role in the mechanism of action of EtOH. This signaling is fundamental for synaptogenesis, which occurs during the third trimester of human pregnancy (first 12 days of life in rats).

METHODS

Acute coronal brain slices were prepared from 7- to 9-day-old rats. Extracellular and patch-clamp electrophysiological recording techniques were used to characterize the acute effects of EtOH on alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR)- and N-methyl-D-aspartate receptor (NMDAR)-mediated responses and long-term potentiation (LTP) in the CA1 hippocampal region.

RESULTS

Ethanol (40 and 80 mM) inhibited AMPAR- and NMDAR-mediated field excitatory postsynaptic potentials (fEPSPs). EtOH (80 mM) also reduced AMPAR-mediated fEPSPs in the presence of an inhibitor of Ca2+ permeable AMPARs. The effect of 80 mM EtOH on NMDAR-mediated fEPSPs was significantly greater in the presence of Mg2+. EtOH (80 mM) neither affected the paired-pulse ratio of AMPAR-mediated fEPSPs nor the presynaptic volley. The paired-pulse ratio of AMPAR-mediated excitatory postsynaptic currents was not affected either, and the amplitude of these currents was inhibited to a lesser extent than that of fEPSPs. EtOH (80 mM) inhibited LTP of AMPAR-mediated fEPSPs.

CONCLUSIONS

Acute EtOH exposure during the third-trimester equivalent of human pregnancy inhibits hippocampal glutamatergic transmission and LTP induction, which could alter synapse refinement and ultimately contribute to the pathophysiology of fetal alcohol spectrum disorder.

Association of markers in the 3' region of the GluR5 kainate receptor subunit gene to alcohol dependence

BACKGROUND

Glutamate neurotransmission plays an important role in a variety of alcohol-related phenomena, including alcohol self-administration by both animals and humans. Because the risk for alcohol dependence (AD) is genetically influenced, genes encoding glutamate receptors are candidates to contribute to the risk for AD. We examined the role of variation in the 3' region of GRIK1, the gene that encodes the GluR5 receptor subunit of the kainic acid glutamate receptor, on risk for AD. We focused specifically on this gene because topiramate, a glutamate modulator that binds to the GluR5 subunit, has shown robust efficacy in the treatment of AD.

METHODS

We genotyped 7 single nucleotide polymorphisms (SNPs) in the 3'-half of GRIK1, which includes 3 differentially spliced exons, in a sample of EA control subjects (n = 507) and subjects with AD (n = 1,057).

RESULTS

We found nominally significant evidence of association to AD for 3 SNPs (rs2832407 in intron 9, rs2186305 in intron 17, and rs2832387 in the 3'UTR). Empirical p-value estimation revealed that only rs2832407 was significantly associated to phenotype (p = 0.043).

DISCUSSION

These findings provide support for the hypothesis that variation in the 3' portion of the gene encoding the GluR5 kainate receptor subunit contributes to the risk for AD. Further research is needed to ascertain whether this SNP is itself functional or whether the association reflects linkage disequilibrium with functional variation elsewhere in the gene and whether this SNP moderates topiramate's effects in the treatment of AD.

Alcohol Pathophysiology

There is no specialized alcohol addiction area in the brain; rather, alcohol acts on a wide range of excitatory and inhibitory nervous networks to modulate neurotransmitters actions by binding with and altering the function of specific proteins. With no hemato-encephalic barrier for alcohol, its actions are strongly related to the amount of intake. Heavy alcohol intake is associated with both structural and functional changes in the central nervous system with long-term neuronal adaptive changes contributing to the phenomena of tolerance and withdrawal. The effects of alcohol on the function of neuronal networks are heterogeneous. Because ethanol affects neural activity in some brain sites but is without effect in others, its actions are analyzed in terms of integrated connectivities in the functional circuitry of neuronal networks, which are of particular interest because of the cognitive interactions discussed in the manuscripts contributing to this review. Recent molecular data are reviewed as a support for the other contributions dealing with cognitive disturbances related to alcohol acute and addicted consumption.

Pharmacogenetics of alcohol and alcohol dependence treatment

In this article, we review studies of genetic moderators of the response to medications to treat alcohol dependence, the acute response to alcohol, and the response to the psychotherapeutic treatment of heavy drinking. We consider four neurotransmitter systems: opioidergic, dopaminergic, GABAergic, and glutamatergic and focus on one receptor protein in each: OPRM1 (the &#micro;-opioid receptor gene), DRD4 (the D(4) dopamine receptor gene), GABRA2 (GABA(A) receptor alpha-2 subunit gene), and GRIK1 (the kainite receptor GluR5 subunit gene). We conclude that because parallel developments in alcoholism treatment and the genetics of alcohol dependence are beginning to converge, using genotypic information, it may be possible to match patients with specific treatments. Of greatest clinical relevance is the finding that the presence of an Asp40 allele in OPRM1 modestly predicts a better response to naltrexone treatment. Promising findings include the observations that a polymorphism in GABRA2 predicts the response to specific psychotherapies; a polymorphism in DRD4 predicts the effects of the antipsychotic olanzapine on craving for alcohol and drinking behavior; and a polymorphism in GRIKI predicts adverse events resulting from treatment with the anticonvulsant topiramate. Although variants in other genes have been associated with the risk for alcohol dependence, they have not been studied as moderators of the response either to treatment or acute alcohol administration. We recommend that, whenever possible, treatment trials include the collection of DNA samples to permit pharmacogenetic analyses, and that such analyses look broadly for relevant genetic variation.

The effects of acute and chronic ethanol exposure on presynaptic and postsynaptic gamma-aminobutyric acid (GABA) neurotransmission in cultured cortical and hippocampal neurons

Decades after ethanol was first described as a gamma-aminobutyric acid (GABA) mimetic, the precise mechanisms that produce the acute effects of ethanol and the physiological adaptations that underlie ethanol tolerance and dependence remain unclear. Although a substantial body of evidence suggests that ethanol acts on GABAergic neurotransmission to enhance inhibition in the central nervous system, the precise mechanisms underlying the physiological effects of both acute and chronic ethanol exposure are still under investigation. We have used in vitro ethanol exposure followed by recording of miniature inhibitory postsynaptic currents (mIPSCs) to determine whether acute or chronic ethanol exposure directly alters synaptic GABA(A) receptor (GABA(A)R) function or GABA release in cultured cortical and hippocampal neurons. Acute ethanol exposure slightly increased the duration of mIPSCs in hippocampal neurons but did not alter mIPSC kinetics in cortical neurons. Acute ethanol exposure did not change mIPSC frequency in either hippocampal or cortical neurons. One day of chronic ethanol exposure produced a transient decrease in mIPSC duration in cortical neurons but did not alter mIPSC kinetics in hippocampal neurons. Chronic ethanol exposure did not change mIPSC frequency in either hippocampal or cortical neurons. Chronic ethanol exposure also did not produce substantial cross-tolerance to a benzodiazepine in either hippocampal or cortical neurons. The results suggest that ethanol exposure in vitro has limited effects on synaptic GABA(A)R function and action potential-independent GABA release in cultured neurons and that ethanol exposure in cultured cortical and hippocampal neurons may not reproduce all the effects that occur in vivo and in acute brain slices.

State-dependent vs. central motor effects of ethanol on breathing

Ethanol, one of the most widely used drugs in Western society, worsens obstructive sleep apnea in humans. No studies, however, have distinguished between two primary mechanisms that could mediate suppression of genioglossus (GG) activity with ethanol. We test the hypothesis that ethanol suppresses GG activity by effects at the hypoglossal motor pool and/or by state-dependent regulation of motor activity via independent influences on sleep/arousal processes. Intraperitoneal injections of ethanol (1.25 g/kg, n = 6 rats) resulted in maximum blood levels of 125.5 +/- 15.8 mg/dl, i.e., physiologically relevant levels for producing behavioral impairment in rats and humans. Ethanol decreased wakefulness, reduced sleep latency, and increased non-rapid eye movement sleep (P < 0.001, n = 10 rats) and significantly reduced postural muscle tone and electroencephalogram frequencies, consistent with sedation. Ethanol also caused a state-dependent (wakefulness only) decrease in respiratory-related GG activity (P = 0.018) but did not affect diaphragm amplitude or rate, with the magnitude of GG decrease related to baseline activity (P < 0.0002). Ethanol did not alter GG activity when applied to the hypoglossal motor pool (0.025-1 M, n = 16 isoflurane-anesthetized rats). In conclusion, ethanol promoted sleep and altered electroencephalogram and postural motor activities, indicative of sedation. The lack of effect on GG with ethanol at the hypoglossal motor pool indicates that the GG and postural motor suppression following systemic administration was mediated via effects on state-dependent/arousal-related processes. These data show that ethanol can suppress GG by primary influences on state-dependent aspects of central nervous system function independent of effects on the respiratory network per se, a distinction that has not previously been identified experimentally.

A case of alcohol withdrawal requiring 1,600 mg of lorazepam in 24 hours

Alcohol withdrawal continues to present significant morbidity and mortality in hospitalized medical/surgical patients. The authors present a case of a patient with delirium tremens requiring up to 1,600 mg/day of lorazepam and discuss alternative treatments for alcohol withdrawal.

Neuroprotection of ethanol against cerebral ischemia/reperfusion induced brain injury through GABA receptor activation

In this study we investigated whether ethanol could play neuroprotective effects against ischemic brain injury and the related mechanism. Cresyl violet staining results demonstrated that moderate dose of ethanol administered intracerebroventricularly (i.c.v.) had neuroprotective effect against ischemia-reperfusion induced neuronal cell death. Ethanol also inhibited the phosphorylation of JNK3 induced by cerebral ischemia-reperfusion. Three separate drugs, NS3763 (the selective antagonist of GluR5), GluR5 antisense oligodeoxynucleotides (AS-ODNs) and Bicuculline (an antagonist of GABA receptors), were found to inhibit the neuroprotective effect of ethanol. Moreover, the GABA receptor agonist muscimol could attenuate the JNK3 phosphorylation. Taken together, the results suggest that during ischemia-reperfusion ethanol may activate presynaptic GluR5-KA and postsynaptic GABA receptors continuously, and the activation of GABA receptors inhibits the JNK3 signal pathway. The results show a novel potential mechanism underlying ethanol protective effects.

Acute alcohol action and desensitization of ligand-gated ion channels

Ethanol exerts its biological actions through multiple receptors, including ion channels. Ion channels that are sensitive to pharmacologically relevant ethanol concentrations constitute a heterogeneous set, including structurally unrelated proteins solely sharing the property that their gating is regulated by a ligand(s). Receptor desensitization is almost universal among these channels, and its modulation by ethanol may be a crucial aspect of alcohol pharmacology and effects in the body. We review the evidence documenting interactions between ethanol and ionotropic receptor desensitization, and the contribution of this interaction to overall ethanol action on channel function. In some cases, such as type 3 serotonin, nicotinic acetylcholine, GABA-A, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors, ethanol actions on apparent desensitization play a significant role in acute drug action on receptor function. In a few cases, mutagenesis helped to identify different areas within a receptor protein that differentially sense n-alcohols, resulting in differential modulation of receptor desensitization. However, desensitization of a receptor is linked to a variety of biochemical processes that may alter protein conformation, such as the lipid microenvironment, post-translational channel modification, and channel subunit composition, the relative contribution of these processes to ethanol interactions with channel desensitization remains unclear. Understanding interactions between ethanol and ionotropic receptor desensitization may help to explain different ethanol actions 1) when ethanol is evaluated in vitro on cloned channel proteins, 2) under physiological or pathological conditions or in distinct cell domains with modified ligand concentration and/or receptor conformation. Finally, receptor desensitization is likely to participate in molecular and, possibly, behavioral tolerance to ethanol, which is thought to contribute to the risk of alcoholism.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

Developmental sensitivity of hippocampal interneurons to ethanol: involvement of the hyperpolarization-activated current, Ih

Ethanol (EtOH) has powerful effects on GABA(A) receptor-mediated neurotransmission, and we have previously shown that EtOH-induced enhancement of GABA(A) receptor-mediated synaptic transmission in the hippocampus is developmentally regulated. Because synaptic inhibition is determined in part by the firing properties of interneurons, we have investigated the mechanisms whereby EtOH influences the spontaneous firing characteristics and hyperpolarization-activated cation current (Ih) of hippocampal interneurons located in the near to the border of stratum lacunosum moleculare and s. radiatum of adolescent and adult rats. EtOH did not affect current injection-induced action potentials of interneurons that do not exhibit spontaneous firing. However, in neurons that fire spontaneously, EtOH enhanced the frequency of spontaneous action potentials (sAPs) in a concentration-dependent manner, an effect that was more pronounced in interneurons from adolescent rats, compared with adult rats. EtOH also modulated the afterhyperpolarization (AHP) that follows sAPs by shortening the tau(slow) decay time constant, and this effect was more pronounced in slices from adolescent rats. EtOH increased Ih amplitudes, accelerated Ih activation kinetics, and increased the maximal Ih conductance in interneurons from animals in both age groups. These effects were also more pronounced in interneurons from adolescents and persisted in the presence of glutamatergic and GABAergic blockers. However, EtOH failed to affect sAP firing in the presence of ZD7288 or cesium chloride. These results suggest that Ih may be of mechanistic significance in the effect of EtOH on interneuron spontaneous firing.

Ethanol inhibition of kainate receptor-mediated excitatory neurotransmission in the rat basolateral nucleus of the amygdala

The neurobiological mechanisms governing alcohol-induced alterations in anxiety-like behaviors are not fully understood. Given that the amygdala is a major emotional center in the brain and regulates the expression of both learned fear and anxiety, neurotransmitter systems within the basolateral amygdala represent likely mechanisms governing the anxiety-related effects of acute ethanol exposure. It is well established that, within the glutamatergic system, N-methyl-d-aspartate (NMDA)-type receptors are particularly sensitive to intoxicating concentrations of ethanol. However, recent evidence suggests that kainate-type glutamate receptors are sensitive to ethanol as well. Therefore, we examined the effect of acute ethanol on kainate receptor (KA-R)-mediated synaptic transmission in the basolateral amygdala (BLA) of Sprague-Dawley rats. Acute ethanol decreased KA-R-mediated excitatory postsynaptic currents (EPSCs) in the BLA in a concentration-dependent manner. Ethanol also inhibited currents evoked by focal application of the kainate receptor agonist (R,S)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA), and ethanol inhibition of kainate EPSCs was not associated with a change in paired-pulse ratio, suggesting a postsynaptic mechanism of ethanol action. The neurophysiological consequences of this acute sensitivity were tested by measuring ethanol's effects on KA-R-dependent modulation of synaptic plasticity. Acute ethanol, like the GluR5-specific antagonist (R,S)-3-(2-carboxybenzyl)willardiine (UBP 296), robustly diminished ATPA-induced increases in synaptic efficacy. Lastly, to better understand the relationship between KA-R activity and anxiety-like behavior, we bilaterally microinjected ATPA directly into the BLA. We observed an increase in measures of anxiety-like behavior, assessed in the light/dark box, with no change in locomotor activity. This evidence suggests that kainate receptors in the BLA are inhibited by pharmacologically relevant concentrations of ethanol and may contribute to some of the acute anxiolytic effects of this drug.

Glutamatergic substrates of drug addiction and alcoholism

The past two decades have witnessed a dramatic accumulation of evidence indicating that the excitatory amino acid glutamate plays an important role in drug addiction and alcoholism. The purpose of this review is to summarize findings on glutamatergic substrates of addiction, surveying data from both human and animal studies. The effects of various drugs of abuse on glutamatergic neurotransmission are discussed, as are the effects of pharmacological or genetic manipulation of various components of glutamate transmission on drug reinforcement, conditioned reward, extinction, and relapse-like behavior. In addition, glutamatergic agents that are currently in use or are undergoing testing in clinical trials for the treatment of addiction are discussed, including acamprosate, N-acetylcysteine, modafinil, topiramate, lamotrigine, gabapentin and memantine. All drugs of abuse appear to modulate glutamatergic transmission, albeit by different mechanisms, and this modulation of glutamate transmission is believed to result in long-lasting neuroplastic changes in the brain that may contribute to the perseveration of drug-seeking behavior and drug-associated memories. In general, attenuation of glutamatergic transmission reduces drug reward, reinforcement, and relapse-like behavior. On the other hand, potentiation of glutamatergic transmission appears to facilitate the extinction of drug-seeking behavior. However, attempts at identifying genetic polymorphisms in components of glutamate transmission in humans have yielded only a limited number of candidate genes that may serve as risk factors for the development of addiction. Nonetheless, manipulation of glutamatergic neurotransmission appears to be a promising avenue of research in developing improved therapeutic agents for the treatment of drug addiction and alcoholism.

Effect of chronic administration of ethanol on the regulation of the delta-subunit of GABA(A) receptors in the rat brain

In the present study, we investigated the effect of chronic ethanol (CE) administration on the polypeptide levels of the delta-subunit of GABA(A) receptors and [(3)H]muscimol binding to the immunoprecipitated delta-subunit-containing GABA(A) receptor assemblies in the rat brain. CE administration resulted a down-regulation of polypeptide levels of the delta-subunit of GABA(A) receptors in the rat cerebellum and hippocampus, whereas there were no changes in the delta-subunit polypeptide levels in the rat cerebral cortex. Further, CE administration caused a down-regulation of native delta-subunit-containing GABA(A) receptor assemblies in the rat cerebellum as determined by [(3)H]muscimol binding to the immunoprecipitated receptor assemblies. These results indicate that the delta-subunit-containing GABA(A) receptors may play a role in chronic ethanol-induced tolerance and dependence.

Blockade of alcohol's amnestic activity in humans by an alpha5 subtype benzodiazepine receptor inverse agonist

Alcohol produces many subjective and objective effects in man including pleasure, sedation, anxiolysis, plus impaired eye movements and memory. In human volunteers we have used a newly available GABA-A/benzodiazepine receptor inverse agonist that is selective for the alpha5 subtype (a5IA) to evaluate the role of this subtype in mediating these effects of alcohol on the brain. After pre-treatment with a5IA, we found almost complete blockade of the marked impairment caused by alcohol (mean breath concentration 150mg/100ml) of word list learning and partial but non-significant reversal of subjective sedation without effects on other measures such as intoxication, liking, and slowing of eye movements. This action was not due to alterations in alcohol kinetics and so provides the first proof of concept that selectively decreasing GABA-A receptor function at a specific receptor subtype can offset some actions of alcohol in humans. It also supports growing evidence for a key role of the alpha5 subtype in memory. Inverse agonists at other GABA-A receptor subtypes may prove able to reverse other actions of alcohol, and so offer a new approach to understanding the actions of alcohol in the human brain and in the treatment of alcohol related disorders in humans.

Ethanol inhibits the sensory responses of cerebellar granule cells in anesthetized cats

BACKGROUND

Granule cells occupy a strategic position in the transmission of afferent information to the cerebellar cortex. They are also the most abundant type of neurons in the cerebellum. The functions of the cerebellum are thought to be sensitive to acute alcohol intoxication. The effects of acute alcohol intoxication on the in vivo physiology of cerebellar granule cells are, however, not completely known.

METHODS

We studied chloralose-anesthetized cats at ethanol doses relevant to human drinking (0.3-1.2 g/kg). We recorded the electrophysiological responses of granule cell clusters to auditory and visual stimulation, and simultaneously monitored the concentration of ethanol in the cerebrospinal fluid (CSF).

RESULTS

At an intravenous ethanol dose of 0.3 g/kg, CSF ethanol concentration peaked in 10 minutes at 17 mM, equivalent to a blood alcohol concentration (BAC) of about 0.08 g/dL. Ethanol quickly and almost completely abolished both auditory and visual responses from granule cells. Complete or near-complete inhibition lasted 15 to 20 minutes; approximately 50% recovery required an additional 15 minutes, and a full recovery yet another 15 minutes. A higher ethanol dose at 1.2 g/kg resulted in a more severe inhibition and required longer time for recovery. The relationship between ethanol dose, CSF ethanol concentration, and granule cell responses was dynamic and nonlinear, critically depending upon the elapsed time.

CONCLUSIONS

Cerebellar granule cell sensory responses are highly sensitive to ethanol inhibition. A rapid development of acute tolerance appears to be a major factor contributing to the dynamic and nonlinear relationship among ethanol dosage, CSF ethanol concentration, and granule cell responses. It is likely that a generalized de-afferentation of the cerebellum from its mossy fiber afferents, followed by the subsequent development of acute tolerance may play major roles by which alcohol intoxication affects cerebellar functions.

Effects of ethanol on excitatory and inhibitory synaptic transmission in rat cortical neurons

BACKGROUND

The gamma-aminobutyric acid-A (GABA(A)) receptor and glutamate receptors are among the most important target sites for the behavioral effects of ethanol. However, data in the literature concerning the ethanol modulation of the GABA(A) and glutamate receptors have been controversial. The activity of the neuronal nicotinic acetylcholine (ACh) receptors (nAChRs) has recently been reported to be potently augmented by ethanol. The activation of nAChRs is also known to cause the release of various neurotransmitters including GABA and glutamate. Thus, ethanol potentiation of nAChRs is expected to stimulate the GABAergic and glutamatergic systems.

METHODS

Whole-cell patch clamp experiments were performed using rat cortical neurons in primary culture to record spontaneous miniature inhibitory postsynaptic currents (mIPSCs) and spontaneous miniature excitatory postsynaptic currents (mEPSCs).

RESULTS

Two types of neurons were distinguished: bipolar neurons possessed alpha4beta2 nAChRs generating a steady current in response to 30 nM ACh, and multipolar neurons that did not generate a current by ACh application. Acetylcholine greatly increased the frequency of mEPSCs and mIPSCs in bipolar neurons but not in multipolar neurons. The amplitude of neither type of neuron was affected by ACh. Ethanol at 10 to 100 mM suppressed the amplitude of mEPSCs while augmenting the amplitude of mIPSCs in both bipolar and multipolar neurons, indicating the direct action on the respective receptors. In bipolar neurons, ACh plus 100 mM ethanol greatly increased the frequency of mIPSCs beyond the levels achieved by ACh alone, while no such increases were observed in multipolar neurons.

CONCLUSIONS

It is concluded that ethanol stimulation of nAChRs modulates the activity of both glutamate and GABA receptors in rat cortical bipolar neurons.

Involvement of non-NMDA glutamate receptors in central amygdala in synaptic actions of ethanol and ethanol-induced reward behavior

The central nucleus of the amygdala (CeA) plays a critical role in positive emotional responses that involve stimulus-reward learning and are induced by the reinforcing effects of many drugs of abuse, including alcohol. Behavioral studies have implicated CeA as a key brain structure in alcohol reward, but the underlying mechanisms are still poorly understood. Recent studies have demonstrated that both NMDA and non-NMDA receptors in CeA neurons are targets of acute and chronic alcohol in naive and alcohol-dependent animals. However, little is known about the role of CeA non-NMDA receptors in synaptic actions of alcohol and, particularly, in the behavior of alcohol reward. In the present study with both whole-cell voltage-clamp recordings in CeA slices in vitro and analysis of an animal model of conditioned place preference (CPP) in vivo, we investigated the synaptic mechanisms for actions of acute and chronic ethanol on CeA non-NMDA receptor functions and their contribution to ethanol-induced reward behavior. Acute ethanol significantly inhibited evoked and miniature synaptic currents mediated by non-NMDA receptors through inhibitions of both postsynaptic non-NMDA receptors and presynaptic glutamate release involving N-type Ca2+ channels. CeA neurons from rats exhibiting the ethanol-induced CPP behavior showed a significant increase in non-NMDA synaptic transmission. Blockade of this increased synaptic transmission through CeA microinjection abolished the CPP behavior. These results suggest that acute alcohol inhibits CeA non-NMDA synaptic transmission through both presynaptic and postsynaptic mechanisms, and chronic alcohol upregulates this synaptic activity, which is required for the alcohol-induced reward behavior.

Low dose acute alcohol effects on GABA A receptor subtypes

GABA(A) receptors (GABA(A)Rs) are the main inhibitory neurotransmitter receptors and have long been implicated in mediating at least part of the acute actions of ethanol. For example, ethanol and GABAergic drugs including barbiturates and benzodiazepines share many pharmacological properties. Besides the prototypical synaptic GABA(A)R subtypes, nonsynaptic GABA(A)Rs have recently emerged as important regulators of neuronal excitability. While high doses (> or =100 mM) of ethanol have been reported to enhance activity of most GABA(A)R subtypes, most abundant synaptic GABA(A)Rs are essentially insensitive to ethanol concentrations that occur during social ethanol consumption (< 30 mM). However, extrasynaptic delta and beta3 subunit-containing GABA(A)Rs, associated in the brain with alpha4 or alpha6 subunits, are sensitive to low millimolar ethanol concentrations, as produced by drinking half a glass of wine. Additionally, we found that a mutation in the cerebellar alpha6 subunit (alpha6R100Q), initially reported in rats selectively bred for increased alcohol sensitivity, is sufficient to produce increased alcohol-induced motor impairment and further increases of alcohol sensitivity in recombinant alpha6beta3delta receptors. Furthermore, the behavioral alcohol antagonist Ro15-4513 blocks the low dose alcohol enhancement on alpha4/6/beta3delta receptors, without reducing GABA-induced currents. In binding assays alpha4beta3delta GABA(A)Rs bind [(3)H]Ro15-4513 with high affinity, and this binding is inhibited, in an apparently competitive fashion, by low ethanol concentrations, as well as analogs of Ro15-4513 that are active to antagonize ethanol or Ro15-4513's block of ethanol. We conclude that most low to moderate dose alcohol effects are mediated by alcohol actions on alcohol/Ro15-4513 binding sites on GABA(A)R subtypes.

Developmental differences in the sensitivity of spontaneous and miniature IPSCs to ethanol

BACKGROUND

Ethanol (EtOH) consumption by juveniles and adolescents is an important public health problem. Recent studies have indicated that adolescent animals are less sedated by EtOH than adult animals and experience less motor impairment. Thus, human adolescents may be able to consume more EtOH prior to sedation, putting them at greater risk for EtOH addiction and other negative consequences of EtOH use. However, the mechanisms underlying this developmental difference are unknown. One contributing factor may be gamma-aminobutyric acid-A (GABA(A)) receptor-mediated inhibition, which is known to produce sedation. We have shown that evoked, GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSCs) are less powerfully enhanced by EtOH in neurons from juvenile or adolescent animals than in those from adult animals; however, the mechanisms of this developmental difference in sensitivity are unknown.

METHODS

Using whole-cell recording, we tested the response of spontaneous and miniature GABA(A) receptor-mediated IPSCs (sIPSCs and mIPSCs) to EtOH in rat hippocampal slices from animals representing two distinct developmental stages: adolescent and adult.

RESULTS

We found significantly greater EtOH-induced enhancement of the frequency of sIPSCs in cells from adult animals compared to those from adolescent animals. Although EtOH also increased the frequency of mIPSCs, this effect was not age dependent. EtOH did not significantly affect the kinetics of mIPSCs.

CONCLUSIONS

We conclude that the sensitivity of GABA(A) receptor-mediated inhibitory processes to EtOH increases with development from the adolescent period to adulthood, and that this is likely mediated by developmental changes in the effect of EtOH on interneuron excitation.