Chronic ethanol administration regulates the expression of GABAA receptor alpha 1 and alpha 5 subunits in the ventral tegmental area and hippocampus

GABAergic mechanisms in alcohol dependence

The target of alcohol's effect on the central nervous system has been sought for more than 50 years in the brain's GABA system. The behavioral and emotional effects of alcohol in humans and rodents are very similar to those of barbiturates and benzodiazepines, and GABAA receptors have been shown to be one of the sites of alcohol action. The mechanisms of GABAergic inhibition have been a hotspot of research but have turned out to be complex and controversial. Genetics support the involvement of some GABAA receptor subunits in the development of alcohol dependence and in alcohol use disorders (AUD). Since the effect of alcohol on the GABAA system resembles that of a GABAergic positive modulator, it may be possible to develop GABAergic drug treatments that could substitute for alcohol. The adaptation mechanisms of the GABA system and the plasticity of the brain are a big challenge for drug development: the drugs that act on GABAA receptors developed so far also may cause adaptation and development of additional addiction. Human polymorphisms should be studied further to get insight about how they affect receptor function, expression or other factors to make reasonable predictions/hypotheses about what non-addictive interventions would help in alcohol dependence and AUD.

Impact of Elevated Brain IL-6 in Transgenic Mice on the Behavioral and Neurochemical Consequences of Chronic Alcohol Exposure

Alcohol consumption activates the neuroimmune system of the brain, a system in which brain astrocytes and microglia play dominant roles. These glial cells normally produce low levels of neuroimmune factors, which are important signaling factors and regulators of brain function. Alcohol activation of the neuroimmune system is known to dysregulate the production of neuroimmune factors, such as the cytokine IL-6, thereby changing the neuroimmune status of the brain, which could impact the actions of alcohol. The consequences of neuroimmune-alcohol interactions are not fully known. In the current studies we investigated this issue in transgenic (TG) mice with altered neuroimmune status relative to IL-6. The TG mice express elevated levels of astrocyte-produced IL-6, a condition known to occur with alcohol exposure. Standard behavioral tests of alcohol drinking and negative affect/emotionality were carried out in homozygous and heterozygous TG mice and control mice to assess the impact of neuroimmune status on the actions of chronic intermittent alcohol (ethanol) (CIE) exposure on these behaviors. The expressions of signal transduction and synaptic proteins were also assessed by Western blot to identify the impact of alcohol-neuroimmune interactions on brain neurochemistry. The results from these studies show that neuroimmune status with respect to IL-6 significantly impacts the effects of alcohol on multiple levels.

Neurological correlates of brain reward circuitry linked to opioid use disorder (OUD): Do homo sapiens acquire or have a reward deficiency syndrome?

The extant literature confirms that an array of polymorphic genes related to- neurotransmitters and second messengers govern the net release of dopamine in the Nucleus Accumbens (NAc) in the mesolimbic region of the brain. They are linked predominantly to motivation, anti-stress, incentive salience (wanting), and wellbeing. Notably, in 2000 the Nobel Prize was awarded to Carlsson, Greengard, and Kandel for their work on the molecular and cellular function of dopaminergic activity at neurons. This historical psychopharmacological work involved neurotransmission of serotonin, endorphins, glutamate, and dopamine, and the seminal work of Blum, Gold, Volkow, Nestler, and others related to neurotransmitter function and related behaviors. Currently, Americans are facing their second and worst opioid epidemic, prescribed opioids, and easy access drive this epidemic of overdoses, and opioid use disorders (OUDs). Presently the clinical consensus is to treat OUD, as if it were an opioid deficiency syndrome, with long-term to life-long opioid substitution therapy. Opioid agonist administration is seen as necessary to replace missing opioids, treat OUD, and prevent overdoses, like insulin is used to treat diabetes. Treatment of OUD and addiction, in general, is similar to the endocrinopathy conceptualization in that it views opioid agonist MATs as an essential core to therapy. Is this approach logical? Other than as harm reduction, is using opioids to treat OUD therapeutic or harmful in the long term? This historical Trieste provides a molecular framework to understand the current underpinnings of endorphinergic/dopaminergic mechanisms related to opioid deficiency syndrome and generalized reward processing depletion. WC 249.

Sex Differences in the Expression of the α5 Subunit of the GABAA Receptor in Alcoholics with and without Cirrhosis of the Liver

BACKGROUND

Alcohol exposure alters the expression of a large number of genes, resulting in neuronal adaptions and neuronal loss, but the underlying mechanisms are largely unknown. miRNAs are gene repressors that are abundant in the brain. A recent study identified ~ 35 miRNAs that are up-regulated in the prefrontal cortex of human alcoholics and predicted to target genes that are down-regulated in the same region. Although interactions between alcohol-responsive miRNAs and their target genes have been predicted, few studies have validated these predictions.

METHODS

We measured the expression of GABA_A α5 mRNA in the prefrontal and motor cortices of human alcoholics and matched controls using real-time PCR. The expression of miR-203 was measured in a subset of these cases. The predicted interaction of miR-203 and GABRA5 was validated for miR-203 using a luciferase reporter assay.

RESULTS

In both frontal and motor cortices, the expression of GABA_A α5 was significantly lower in cirrhotic alcoholics compared with controls. Further, the pattern of expression between the groups was significantly different between males and females. The expression of miR-203 was higher in the prefrontal cortex of cirrhotic alcoholics compared with controls and uncomplicated alcoholics. These differences were particularly marked in female cases. Cotransfection of GABRA5 with miR-203 in HEK293T cells reduced luciferase reporter activity.

CONCLUSION

There are sex differences in the expression of GABA_A α5 and miR-203 in the brain of human alcoholics which are particularly marked in alcoholics with cirrhosis of the liver. Further, miR-203 may mediate the changes in expression of this GABA_A receptor isoform that is brought about by alcohol exposure.

Transplantation of fecal microbiota from patients with alcoholism induces anxiety/depression behaviors and decreases brain mGluR1/PKC ε levels in mouse

Recent studies have revealed that the gut microbiota participates in the psychiatric behavior changes in disorders associated with alcohol. But it still remains unknown whether alcoholism is involved in changes in gut microbiota and its underlying mechanism is also not clear. Here, we tested the gut microbiota of patients with alcoholism and conducted fecal microbiota transplantation (FMT) from patients with alcoholism to C57BL/6J mice whose gut microbiota had been sharply suppressed with antibiotics (ABX). Then we evaluated their alcohol preference degree, anxiety, and depression-like behaviors and social interaction behaviors, together with molecular changes in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc). Our data indicated that the gut microbiota of patients with alcoholism was drastically different from those of the healthy adults. The abundance of p_Firmicutes was significantly increased whereas p_Bacteroidetes was decreased. Compared to mice transplanted with fecal microbiota from healthy male adults, the mice accepting fecal microbiota from patients with alcoholism showed (a) anxiety-like and depression-like behaviors, (b) decreased social interaction behaviors, (c) spontaneous alcohol preference, and (d) decreased brain-derived neurotrophic factor (BDNF), alpha 1 subunit of GABA type A receptor (α1GABA_A R) in mPFC and decreased metabotropic glutamate receptors 1 (mGluR1), protein kinase C (PKC) ε in NAc. Overall, our results suggest that fecal microbiota from patients with alcoholism did induce a status like alcohol dependence in C57BL/6J mice. The decreased expression of BDNF, α1GABA_A R, and mGluR1/ PKC ε may be the underlying mechanism.

GABA-Aα5 Might Be Involved in Learning-Memory Dysfunction in the Offsprings of Chronic Ethanol-Treated Rats via GABA-Aα5 Histone H3K9 Acetylation

Recently, numerous studies have been focused on the relationship between GABA-A receptors and alcohol-induced spatial learning and memory deficits. GABA-Aα5, a subunit of GABA-A receptors, is considered to play an important role in alcohol-induced cognitive impairment, however, the mechanism remains obscure. In this study, we found that the expression of GABA-Aα5 increased in rats treated with chronic ethanol via histone H3K9 acetylation. Furthermore, this epigenetic modification could be inherited by the next generations, which eventually exhibit similar spatial learning and memory deficits in the offsprings. In summary, our results suggested that GABA-Aα5 might be involved in chronic ethanol treatment-induced learning-memory dysfunction and for the first time proved that learning-memory dysfunction could be inherited by the offsprings via histone H3K9 acetylation. Hopefully, in the near future, GABA-Aα5 inhibitors would be an effective way to treat alcohol-induced cognition impairment.

α5GABAA subunit-containing receptors and sweetened alcohol cue-induced reinstatement and active sweetened alcohol self-administration in male rats

RATIONALE

GABA_A receptors containing the α5 subunit (i.e., α5GABA_A receptors) appear to be critically involved in the reinforcing and subjective effects of alcohol. Their role in alcohol relapse remains unknown.

OBJECTIVES

Pharmacological approaches were used to probe the role of α5GABA_A receptors in alcohol seeking induced by re-exposure to a sweetened alcohol-paired cue, as well as in alcohol + sucrose vs. sucrose self-administration.

METHODS

For reinstatement studies, rats were trained to self-administer alcohol under a fixed-ratio schedule in which responding was maintained by alcohol + sucrose deliveries and an alcohol-paired stimulus. Sweetened alcohol seeking was extinguished by eliminating solution deliveries and the sweetened alcohol-paired stimulus. During reinstatement tests, animals received pretreatments of an α5GABA_A inverse agonist (L-655,708) or an agonist (QH-ii-066) prior to sessions in which presentation of the sweetened alcohol-paired stimulus was restored, but no solution was delivered. For self-administration studies, rats were trained to self-administer alcohol + sucrose or sucrose under a fixed-ratio schedule. Once stable, animals received pretreatments of QH-ii-066, L-655,708, the inverse agonist RY-023, or naltrexone.

RESULTS

L-655,708 attenuated reinstatement of sweetened alcohol seeking by alcohol + sucrose-paired cues; whereas sweetened alcohol-seeking behavior was augmented by QH-ii-066, albeit at different doses in different rats. Both L-655,708 and RY-023 selectively reduced alcohol + sucrose vs. sucrose self-administration. In contrast, naltrexone reduced both alcohol + sucrose and sucrose self-administration; whereas QH-ii-066 enhanced sucrose self-administration only.

CONCLUSIONS

α5GABA_A receptors play a key role in the modulation of sweetened alcohol cue-induced reinstatement, as well as in alcohol + sucrose but not sucrose self-administration. Inverse agonist activity at α5GABA_A receptors may offer a novel strategy for both the reduction of problematic drinking and the prevention of relapse.

Chronic alcohol exposure induced gut microbiota dysbiosis and its correlations with neuropsychic behaviors and brain BDNF/Gabra1 changes in mice

Alcohol addiction can cause brain dysfunction and many other diseases. Recently, increasing evidences have suggested that gut microbiota plays a vital role in regulating alcohol addiction. However, the exact mechanism has not yet been elucidated. Here, our study focused on the intestinal bacteria alternations and their correlations with alcohol-induced neuropsychic behaviors. When consuming alcohol over 3-week period, animals gradually displayed anxiety/depression-like behaviors. Moreover, 16S rRNA sequencing showed significant intestinal microflora dysbiosis and distinct community composition. Actinobacteria and Cyanobacteria were both increased at the phylum level. At the genus level, Adlercreutzia spp., Allobaculum spp., and Turicibacter spp. were increased whereas Helicobacter spp. was decreased. We also found that the distances in inner zone measured by open field test and 4% (v/v) alcohol preference percentages were significantly correlated with Adlercreutzia spp. The possible mechanisms were explored and we found the expression of brain-derived neurotrophic factor (BDNF) and α1 subunit of γ-aminobutyric acid A receptor (Gabra1) were both decreased in prefrontal cortex (PFC). Especially, further correlation analyses demonstrated that decreased Adlercreutzia spp. was positively correlated with alcohol preference and negatively correlated with anxiety-like behavior and BDNF/Gabra1 changes in PFC. Similar relationships were observed between Allobaculum spp. and alcohol preference and BDNF changes. Helicobacter spp. and Turicibacter spp. were also correlated with PFC BDNF and hippocampus Gabra1 level. Taken together, our study showed that gut microbiota dysbiosis during chronic alcohol exposure was closely correlated with alcohol-induced neuropsychic behaviors and BDNF/Gabra1 expression, which provides a new perspective for understanding underlying mechanisms in alcohol addiction. © 2018 BioFactors, 45(2):187-199, 2019.

An Emerging Circuit Pharmacology of GABAA Receptors

In the past 20 years we have learned a great deal about GABA_A receptor (GABA_AR) subtypes, and which behaviors are regulated or which drug effects are mediated by each subtype. However, the question of where GABA_ARs involved in specific drug effects and behaviors are located in the brain remains largely unanswered. We review here recent studies taking a circuit pharmacology approach to investigate the functions of GABA_AR subtypes in specific brain circuits controlling fear, anxiety, learning, memory, reward, addiction, and stress-related behaviors. The findings of these studies highlight the complexity of brain inhibitory systems and the importance of taking a subtype-, circuit-, and neuronal population-specific approach to develop future therapeutic strategies using cell type-specific drug delivery.

Altered brain activity during withdrawal from chronic alcohol is associated with changes in IL-6 signal transduction and GABAergic mechanisms in transgenic mice with increased astrocyte expression of IL-6

Interleukin-6 (IL-6) is an important neuroimmune factor that is increased in the brain by alcohol exposure/withdrawal and is thought to play a role in the actions of alcohol on the brain. To gain insight into IL-6/alcohol/withdrawal interactions and how these interactions affect the brain, we are studying the effects of chronic binge alcohol exposure on transgenic mice that express elevated levels of IL-6 in the brain due to increased astrocyte expression (IL-6 tg) and their non-transgenic (non-tg) littermate controls. IL-6/alcohol/withdrawal interactions were identified by genotypic differences in spontaneous brain activity in electroencephalogram (EEG) recordings from the mice, and by Western blot analysis of protein activation or expression in hippocampus obtained from the mice after the final alcohol withdrawal period. Results from EEG studies showed frequency dependent genotypic differences in brain activity during withdrawal. For EEG frequencies that were affected by alcohol exposure/withdrawal in both genotypes, the nature of the effect was similar, but differed across withdrawal cycles. Differences between IL-6 tg and non-tg mice were also observed in Western blot studies of the activated form of STAT3 (phosphoSTAT3), a signal transduction partner of IL-6, and subunits of GABA_A receptors (GABA_AR). Regression analysis revealed that pSTAT3 played a more prominent role during withdrawal in the IL-6 tg mice than in the non-tg mice, and that the role of GABA_AR alpha-5 and GABA_AR alpha-1 in brain activity varied across genotype and withdrawal. Taken together, our results suggest that IL-6 can significantly impact mechanisms involved in alcohol withdrawal.

Ventral Tegmental Area GABA Neurons Are Resistant to GABA(A) Receptor-Mediated Inhibition During Ethanol Withdrawal

The neural mechanisms underlying alcohol dependence are not well-understood. GABAergic neurons in the ventral tegmental area (VTA) are a relevant target for ethanol. They are inhibited by ethanol at physiologically-relevant levels in vivo and display marked hyperexcitability during withdrawal. In the present study, we examined the effects of the GABA(A) receptor agonist muscimol on VTA neurons ex vivo following withdrawal from acute and chronic ethanol exposure. We used standard cell-attached mode electrophysiology in the slice preparation to evaluate the effects of muscimol on VTA GABA neuron firing rate following exposure to acute and chronic ethanol in male CD-1 GAD-67 GFP mice. In the acute condition, the effect of muscimol on VTA neurons was evaluated 24 h and 7 days after a single in vivo dose of saline or ethanol. In the chronic condition, the effect of muscimol on VTA neurons was evaluated 24 h and 7 days after either 2 weeks of twice-daily IP ethanol or saline or following exposure to chronic intermittent ethanol (CIE) vapor or air for 3 weeks. VTA GABA neuron firing rate was more sensitive to muscimol than DA neuron firing rate. VTA GABA neurons, but not DA neurons, were resistant to the inhibitory effects of muscimol recorded 24 h after a single ethanol injection or chronic ethanol exposure. Administration of the NMDA receptor antagonist MK-801 before ethanol injection restored the sensitivity of VTA GABA neurons to muscimol inhibition. Seven days after ethanol exposure, VTA GABA neuron firing rate was again susceptible to muscimol's inhibitory effects in the acute condition, but the resistance persisted in the chronic condition. These findings suggest that VTA GABA neurons exclusively undergo a shift in GABA(A) receptor function following acute and chronic exposure. There appears to be transient GABA(A) receptor-mediated plasticity after a single exposure to ethanol that is mediated by NMDA glutamate receptors. In addition, the resistance to muscimol inhibition in VTA GABA neurons persists in the dependent condition, which may contribute to the the hyperexcitability of VTA GABA neurons and inhibition of VTA DA neurons during withdrawal as well as the motivation to seek alcohol.

CRF modulates glutamate transmission in the central amygdala of naïve and ethanol-dependent rats

Corticotropin-releasing factor (CRF) signaling in the central nucleus of the amygdala (CeA) is hypothesized to drive the development of alcohol dependence, as it regulates ethanol intake and several anxiogenic behaviors linked to withdrawal. Excitatory glutamatergic neurotransmission contributes to alcohol reinforcement, tolerance and dependence. Therefore, in this study we used in vitro slice electrophysiology to investigate the effects of CRF and its receptor subtype (CRF₁ and CRF₂) antagonists on both evoked and spontaneous action potential-independent glutamatergic transmission in the CeA of naive and ethanol-dependent Sprague-Dawley rats. We found that CRF (25-200 nM) concentration-dependently diminished evoked compound excitatory postsynaptic potentials (EPSPs), but increased miniature excitatory postsynaptic current (mEPSC) frequencies similarly in CeA neurons of both naïve and ethanol-dependent rats, indicating reduced evoked glutamatergic responses and enhanced vesicular glutamate release, respectively. This CRF-induced vesicular glutamate release was prevented by the CRF_1/2 antagonist (Astressin B) and the CRF₁ antagonist (R121919), but not by the CRF₂ antagonist (Astressin 2B). Similarly, CRF's effects on evoked glutamatergic responses were completely blocked by CRF₁ antagonism, but only slightly decreased in the presence of the CRF₂ antagonist. Moreover, CRF₁ antagonism reveals a tonic facilitation of vesicular glutamate, whereas the CRF₂ antagonism revealed a tonic inhibition of vesicular glutamate release. Collectively our data show that CRF primarily acts at presynaptic CRF₁ to produce opposite effects on CeA evoked and spontaneous glutamate release and that the CRF system modulates CeA glutamatergic synapses throughout the development of alcohol dependence.

Synaptic targets: Chronic alcohol actions

Alcohol acts on numerous cellular and molecular targets to regulate neuronal communication within the brain. Chronic alcohol exposure and acute withdrawal generate prominent neuroadaptations at synapses, including compensatory effects on the expression, localization and function of synaptic proteins, channels and receptors. The present article reviews the literature describing the synaptic effects of chronic alcohol exposure and their relevance for synaptic transmission in the central nervous system. This review is not meant to be comprehensive, but rather to highlight the effects that have been observed most consistently and that are thought to contribute to the development of alcohol dependence and the negative aspects of withdrawal. Specifically, we will focus on the major excitatory and inhibitory neurotransmitters in the brain, glutamate and GABA, respectively, and how their neuroadaptations after chronic alcohol exposure contributes to alcohol reinforcement, dependence and withdrawal. This article is part of the Special Issue entitled "Alcoholism".

Using [(11)C]Ro15 4513 PET to characterise GABA-benzodiazepine receptors in opiate addiction: Similarities and differences with alcoholism

The importance of the GABA-benzodiazepine receptor complex and its subtypes are increasingly recognised in addiction. Using the α1/α5 benzodiazepine receptor PET radioligand [¹¹C]Ro15 4513, we previously showed reduced binding in the nucleus accumbens and hippocampus in abstinent alcohol dependence. We proposed that reduced [¹¹C]Ro15 4513 binding in the nucleus accumbens was a marker of addiction whilst the reduction in hippocampus and positive relationship with memory was a consequence of chronic alcohol abuse. To examine this further we assessed [¹¹C]Ro15 4513 binding in another addiction, opiate dependence, and used spectral analysis to estimate contributions of α1 and α5 subtypes to [¹¹C]Ro15 4513 binding in opiate and previously acquired alcohol-dependent groups. Opiate substitute maintained opiate-dependent men (n = 12) underwent an [¹¹C]Ro15 4513 PET scan and compared with matched healthy controls (n = 13). We found a significant reduction in [¹¹C]Ro15 4513 binding in the nucleus accumbens in the opiate-dependent compared with the healthy control group. There was no relationship between [¹¹C]Ro15 4513 binding in the hippocampus with memory. We found that reduced [¹¹C]Ro15 4513 binding was associated with reduced α5 but not α1 subtypes in the opiate-dependent group. This was also seen in an alcohol-dependent group where an association between memory performance and [¹¹C]Ro15 4513 binding was primarily driven by α5 and not α1 subtype. We suggest that reduced α5 levels in the nucleus accumbens are associated with addiction since we have now shown this in dependence to two pharmacologically different substances, alcohol and opiates.

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Lower [¹¹C]Ro15 4513 binding is evident in the nucleus accumbens of opiate addicts.

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This appears primarily due to lower levels of α5 subtype of the GABA-A receptor.

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Lower [¹¹C]Ro15 4513 binding is similarly found in alcoholism.

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Lower levels of α5 GABA-A receptor in nucleus accumbens may underpin addiction.

Thinking after Drinking: Impaired Hippocampal-Dependent Cognition in Human Alcoholics and Animal Models of Alcohol Dependence

Alcohol use disorder currently affects approximately 18 million Americans, with at least half of these individuals having significant cognitive impairments subsequent to their chronic alcohol use. This is most widely apparent as frontal cortex-dependent cognitive dysfunction, where executive function and decision-making are severely compromised, as well as hippocampus-dependent cognitive dysfunction, where contextual and temporal reasoning are negatively impacted. This review discusses the relevant clinical literature to support the theory that cognitive recovery in tasks dependent on the prefrontal cortex and hippocampus is temporally different across extended periods of abstinence from alcohol. Additional studies from preclinical models are discussed to support clinical findings. Finally, the unique cellular composition of the hippocampus and cognitive impairment dependent on the hippocampus is highlighted in the context of alcohol dependence.

A review on alcohol: from the central action mechanism to chemical dependency

SummaryIntroduction:alcohol is a psychotropic depressant of the central nervous system (CNS) that promotes simultaneous changes in several neuronal pathways, exerting a profound neurological impact that leads to various behavioral and biological alterations.Objectives:to describe the effects of alcohol on the CNS, identifying the signaling pathways that are modified and the biological effects resulting from its consumption.Methods:a literature review was conducted and articles published in different languages over the last 15 years were retrieved.Results:the studies reviewed describe the direct effect of alcohol on several neurotransmitter receptors (gamma-aminobutyric acid [GABA], glutamate, endocannabinoids AEA and 2-AG, among others), the indirect effect of alcohol on the limbic and opioid systems, and the effect on calcium and potassium channels and on proteins regulated by GABA in the hippocampus.Discussion and conclusion:the multiple actions of alcohol on the CNS result in a general effect of psychomotor depression, difficulties in information storage and logical reasoning and motor incoordination, in addition to stimulating the reward system, a fact that may explain the development of addiction. Knowledge on the neuronal signaling pathways that are altered by alcohol allows the identification of effectors which could reduce its central action, thus, offering new therapeutic perspectives for the rehabilitation of alcohol addicts.

Adolescent alcohol exposure alters GABAA receptor subunit expression in adult hippocampus

BACKGROUND

The long-term consequences of adolescent alcohol abuse that persist into adulthood are poorly understood and have not been widely investigated. We have shown that intermittent exposure to alcohol during adolescence decreased the amplitude of GABAA receptor (GABAA R)-mediated tonic currents in hippocampal dentate granule cells in adulthood. The aim of this study was to investigate the enduring effects of chronic intermittent alcohol exposure during adolescence or adulthood on the expression of hippocampal GABAA Rs.

METHODS

We used a previously characterized tissue fractionation method to isolate detergent resistant membranes and soluble fractions, followed by Western blots to measure GABAA R protein expression. We also measured mRNA levels of GABAA R subunits using quantitative real-time polymerase chain reaction.

RESULTS

Although the protein levels of α1-, α4-, and δ-GABAA R subunits remained stable between postnatal day (PD) 30 (early adolescence) and PD71 (adulthood), the α5-GABAA R subunit was reduced across that period. In rats that were subjected to adolescent intermittent ethanol (AIE) exposure between PD30 and PD46, there was a significant reduction in the protein levels of the δ-GABAA R, in the absence of any changes in mRNA levels, at 48 hours and 26 days after the last ethanol (EtOH) exposure. Protein levels of the α4-GABAA R subunit were significantly reduced, but mRNA levels were increased, 26 days (but not 48 hours) after the last AIE exposure. Protein levels of α5-GABAA R were not changed by AIE, but mRNA levels were reduced at 48 hours but normalized 26 days after AIE. In contrast to the effects of AIE, chronic intermittent ethanol (CIE) exposure during adulthood had no effect on expression of any of the GABAA R subunits examined.

CONCLUSIONS

AIE produced both short- and long-term alterations of GABAA R subunits mRNA and protein expression in the hippocampus, whereas CIE produced no long-lasting effects on those measures. The observed reduction of protein levels of the δ-GABAA R, specifically, is consistent with previously reported altered hippocampal GABAA R-mediated electrophysiological responses after AIE. The absence of effects of CIE underscores the emerging view of adolescence as a time of distinctive vulnerability to the enduring effects of repeated EtOH exposure.

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.

Molecular and neurologic responses to chronic alcohol use

This chapter provides an overview of current knowledge on the molecular and clinical aspects of chronic alcohol effects on the central nervous system. This drug is almost ubiquitous, widely enjoyed socially, but produces a diverse spectrum of neurologic disease when abused. Acutely, alcohol interacts predominantly with γ-aminobutyric acid-A (GABA-A) and N-methyl-d-aspartate (NMDA) receptors, but triggers diverse signaling events within well-defined neural pathways. These events result in adaptive changes in gene expression that ultimately produce two major states: addiction and toxicity. Epigenetic modifications of chromatin could lead to long-lived or even transgenerational changes in gene expression, thus producing aspects of the heritability of alcohol use disorders (AUD) and long-term behaviors such as recidivism. The diverse clinical syndromes produced by chronic alcohol actions in the central nervous system reflect the molecular pathology and predominantly involve aspects of tolerance/withdrawal, selective vulnerability (manifest as central pontine myelinolysis, Marchiafava-Bignami disease), and additional environmental factors (e.g., thiamine deficiency in Wernicke-Korsakoff's syndrome). Additionally, deleterious aspects of chronic alcohol on signaling, synaptic transmission, and cell toxicity lead to primary alcoholic dementia. Genetically determined aspects of myelin structure and alcohol actions on myelin gene expression may be a prominent molecular mechanism resulting in a predisposition to, or causation of, AUD and multiple other neurologic complications of chronic alcohol. The dramatic progress made in understanding molecular actions of alcohol holds great promise for our eventual treatment or prevention of AUD and neurologic complications resulting from chronic alcohol abuse.

Potential substrates for nicotine and alcohol interactions: a focus on the mesocorticolimbic dopamine system

Epidemiological studies consistently find correlations between nicotine and alcohol use, yet the neural mechanisms underlying their interaction remain largely unknown. Nicotine and alcohol (i.e., ethanol) share many common molecular and cellular targets that provide potential substrates for nicotine-alcohol interactions. These targets for interaction often converge upon the mesocorticolimbic dopamine system, where the link to drug self-administration and reinforcement is well documented. Both nicotine and alcohol activate the mesocorticolimbic dopamine system, producing downstream dopamine signals that promote the drug reinforcement process. While nicotine primarily acts via nicotinic acetylcholine receptors, alcohol acts upon a wider range of receptors and molecular substrates. The complex pharmacological profile of these two drugs generates overlapping responses that ultimately intersect within the mesocorticolimbic dopamine system to promote drug use. Here we will examine overlapping targets between nicotine and alcohol and provide evidence for their interaction. Based on the existing literature, we will also propose some potential targets that have yet to be directly tested. Mechanistic studies that examine nicotine-alcohol interactions would ultimately improve our understanding of the factors that contribute to the associations between nicotine and alcohol use.

Synaptic effects induced by alcohol

Ethanol (EtOH) has effects on numerous cellular molecular targets, and alterations in synaptic function are prominent among these effects. Acute exposure to EtOH activates or inhibits the function of proteins involved in synaptic transmission, while chronic exposure often produces opposing and/or compensatory/homeostatic effects on the expression, localization, and function of these proteins. Interactions between different neurotransmitters (e.g., neuropeptide effects on release of small molecule transmitters) can also influence both acute and chronic EtOH actions. Studies in intact animals indicate that the proteins affected by EtOH also play roles in the neural actions of the drug, including acute intoxication, tolerance, dependence, and the seeking and drinking of EtOH. This chapter reviews the literature describing these acute and chronic synaptic effects of EtOH and their relevance for synaptic transmission, plasticity, and behavior.

A [11C]Ro15 4513 PET study suggests that alcohol dependence in man is associated with reduced α5 benzodiazepine receptors in limbic regions

Preclinical evidence suggests the α5 subtype of the GABA-benzodiazepine receptor is involved in some of the actions of alcohol and in memory. The positron emission tomography (PET) tracer, [(11)C]Ro15 4513 shows relative selectivity in labelling the α5 subtype over the other GABA-benzodiazepine receptor subtypes in limbic regions of the brain. We used this tracer to investigate the distribution of α5 subtype availability in human alcohol dependence and its relationship to clinical variables. Abstinent (>6 weeks) alcohol-dependent men and healthy male controls underwent an [(11)C]Ro15 4513 PET scan. We report [(11)C]Ro15 4513 brain uptake for 8 alcohol-dependent men and 11 healthy controls. We found a significant reduction in [(11)C]Ro15 4513 binding in the nucleus accumbens, parahippocampal gyri, right hippocampus and amygdala in the alcohol-dependent compared with the healthy control group. Levels of [(11)C]Ro15 4513 binding in both hippocampi were significantly and positively associated with performance on a delayed verbal memory task in the alcohol-dependent but not the control group. We speculate that the reduced limbic [(11)C]Ro15 4513 binding seen here results from the effects of alcohol, though we cannot currently distinguish whether they are compensatory in nature or evidence of brain toxicity.

Zebrafish: a model for the study of addiction genetics

Drug abuse and dependence are multifaceted disorders with complex genetic underpinnings. Identifying specific genetic correlates is challenging and may be more readily accomplished by defining endophenotypes specific for addictive disorders. Symptoms and syndromes, including acute drug response, consumption, preference, and withdrawal, are potential endophenotypes characterizing addiction that have been investigated using model organisms. We present a review of major genes involved in serotonergic, dopaminergic, GABAergic, and adrenoreceptor signaling that are considered to be directly involved in nicotine, opioid, cannabinoid, and ethanol use and dependence. The zebrafish genome encodes likely homologs of the vast majority of these loci. We also review the known expression patterns of these genes in zebrafish. The information presented in this review provides support for the use of zebrafish as a viable model for studying genetic factors related to drug addiction. Expansion of investigations into drug response using model organisms holds the potential to advance our understanding of drug response and addiction in humans.

Ethanol-induced loss-of-righting response during ethanol withdrawal in male and female rats: associations with alterations in Arc labeling

BACKGROUND

There is increasing evidence for relevant sex differences in responses to ethanol. Several investigations have found differences in expression and recovery from ethanol withdrawal (EW) in people and across various animal models. We have found that female rats recover more quickly than male rats and show differential responses to various behavioral assessments and pharmacological challenges during withdrawal. The purpose of this study was to determine whether sex differences in EW behaviors extend to the hypnotic effects of acute ethanol administration.

METHODS

We used a repeated measures design to assess duration and latency for loss-of-righting reflex following an acute injection of ethanol (4.2 g/kg; 20% w/v) to pair-fed control or ethanol-withdrawn animals at 1 and 3 days EW in male, female, and ovariectomized female (OVX) rats. We determined protein levels of the activity-regulated cytoskeletal protein (Arc), used as a marker for synaptic activity in glutamatergic synapses, in the motor cortex and prefrontal cortex across these same treatment conditions.

RESULTS

Ethanol-withdrawn animals had a reduced ethanol-induced sleep time compared to controls at 1 day EW. Sleep time remained shortened at 3 days EW for males and OVX, but not females. Arc protein levels in motor cortex and preoptic nuclei significantly increased at 1 day EW across all sex conditions, suggestive of an association with the reduced ethanol-induced sleep times during EW. Arc levels increased further for males and OVX, but not females, at the 3 days EW time point.

CONCLUSIONS

These findings add further support to sex differences in effects of and responses to ethanol. They suggest that the more rapid recovery from EW for females than males also includes expression of tolerance to the hypnotic effects of ethanol. These sex differences may involve some differential neuroadaptations in glutamatergic signaling.

Effects of 7-keto dehydroepiandrosterone on voluntary ethanol intake in male rats

Administration of dehydroepiandrosterone (DHEA), a neurosteroid that can negatively modulate the GABA A receptor, has been shown to decrease voluntary intake of ethanol in rats. In vivo, DHEA can be metabolized to a variety of metabolites, including 3β-acetoxyandrost-5-ene-7,17-dione (7-keto DHEA), a metabolite without the prohormonal effects of DHEA. This study compared the effectiveness of 7-keto DHEA with DHEA for reducing ethanol intake in the same group of rats. The subjects, previously trained to drink ethanol using a saccharin-fading procedure, had access to ethanol for 30 min daily and the amount consumed was recorded. Subjects were administered 10 and 56 mg/kg of DHEA or 7-keto DHEA intraperitoneally 15 min before drinking sessions. Subjects received each particular dose daily until one of two criteria was met, that is, either ethanol intake did not differ by more than 20% of the mean for 3 consecutive days or for a maximum of 8 days. Both 10 and 56 mg/kg of 7-keto DHEA significantly reduced the dose of ethanol consumed. Although 10mg/kg of 7-keto DHEA produced decreases similar to those found with DHEA, the 56-mg/kg dose of 7-keto DHEA was significantly more effective at decreasing the dose of ethanol consumed than the same dose of DHEA. These results show that 7-keto DHEA is comparable with, or possibly more effective than, DHEA at decreasing ethanol consumption in rats, and that 7-keto DHEA is a compound deserving further investigation as a possible clinical treatment for alcohol abuse without the prohormonal effects of DHEA.

Actions of two GABAA receptor benzodiazepine-site ligands that are mediated via non-γ2-dependent modulation

The potent sedative-hypnotic zolpidem and the convulsant methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM) act primarily by binding to the benzodiazepine site of the main inhibitory neurotransmitter receptor, the pentameric γ-aminobutyric acid type A receptor (GABA(A)). This binding depends critically on the wild-type F77 residue of the GABA(A) receptor γ2 subunit. Mice with γ2 subunit F77I point mutation (γ2I77 mouse line) lose the high-affinity nanomolar binding of these ligands as well as their most robust behavioral actions at low doses. Interestingly, the γ2I77 mice offer a tool to study the actions of these substances mediated via other possible binding sites of the GABA(A) receptor. In ligand autoradiographic experiments, we discovered in γ2I77 mouse brain sections a significant amount of residual non-γ2 subunit-dependent benzodiazepine site binding enriched to the striatum and septum. Zolpidem only weakly affected this residual binding at micromolar concentrations, and only a high zolpidem dose (≥ 40 mg/kg) caused sedation and deficits in motor coordination in γ2I77 mice. DMCM had an agonistic action through a secondary, low-affinity non-benzodiazepine binding site of the GABA(A) receptor in the forebrain of γ2I77 mice, and this drug also fully displaced the residual benzodiazepine-site labeling. In behavioral tests, a high dose (20mg/kg) of DMCM was sedative and modulated fear learning. DMCM, but not zolpidem, acted as an agonist in recombinant GABA(A) α1/6β3 receptors studied using ligand binding and electrophysiological assays. Our results highlight the less well-known actions of high doses of DMCM and zolpidem that are not mediated via the γ2 subunit-containing benzodiazepine site of the GABA(A) receptor.

Neuroimaging insights into the role of cortical GABA systems and the influence of nicotine on the recovery from alcohol dependence

This paper reviews evidence suggesting that nicotine and tobacco smoke profoundly modulate the effects of alcohol on γ-aminobutyric acid (GABA) neuronal function, specifically at the GABA(A)-benzodiazepine receptor (GABA(A)-BZR). The focus of this paper is on recent neuroimaging evidence in preclinical models as well as clinical experiments. First, we review findings implicating the role of alcohol at the GABA(A)-BZR and discuss the changes in GABA(A)-BZR availability during acute and prolonged alcohol withdrawal. Second, we discuss preclinical evidence that suggests nicotine affects GABA neuronal function indirectly by a primary action at neuronal nicotinic acetylcholine receptors. Third, we show how this evidence converges in studies that examine GABA levels and GABA(A)-BZRs in alcohol-dependent smokers and nonsmokers, suggesting that tobacco smoking attenuates the chemical changes that occur during alcohol withdrawal. Based on a comprehensive review of literature, we hypothesize that tobacco smoking minimizes the changes in GABA levels that typically occur during the acute cycles of drinking in alcohol-dependent individuals. Thus, during alcohol withdrawal, the continued tobacco smoking decreases the severity of the withdrawal-related changes in GABA chemistry. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Ethanol-induced locomotor sensitization in DBA/2J mice is associated with alterations in GABA(A) subunit gene expression and behavioral sensitivity to GABA(A) acting drugs

Repeated exposure to ethanol may produce increased sensitivity to its acute locomotor stimulant actions, a process referred to as locomotor sensitization. Neuroadaptation within certain brain circuits, including those possessing GABA(A) receptors, may underlie locomotor sensitization to ethanol. Indeed, GABA(A) receptors are documented mediators of ethanol's cellular and behavioral actions. Moreover, because subunit composition of this receptor is predictive of its pharmacology, it is possible that alterations in subunit composition contribute to the expression of locomotor sensitization to ethanol. The goal of the present study was to determine if alterations in GABA(A) subunit composition are associated with the expression of locomotor sensitization in DBA/2J mice, a strain known to be particularly susceptible to the development of this behavioral phenomenon. Following a modified 14day sensitization procedure (Phillips et al., 1994) relative changes in GABA(A) subunit gene expression were assessed in discrete mesolimbic brain regions. To determine if the observed changes in gene expression produced functional changes in the locomotor responses to drugs known to either preferentially or generally activate GABA(A) receptors normally possessing the significantly altered subunits, separate cohorts of animals were challenged with one of several low doses of zolpidem (alpha1-selective), etomidate (beta2/3-selective), or flurazepam (gamma2-directed) and assessed for locomotor alterations. Sensitized animals displayed increased expression of the alpha1, beta2, and gamma2 (v1) subunits in the Nucleus Accumbens (NAc) but not Ventral Tegmental Area (VTA). Additionally, sensitized animals displayed altered sensitivity to the locomotor actions of etomidate and flurazepam. These results support the hypothesis that neuroadaptive changes in GABA(A) subunit composition participate in the expression of locomotor sensitization.

Regulation of GABA(A) receptor subunit expression by pharmacological agents

The gamma-aminobutyric acid (GABA) type A receptor system, the main fast-acting inhibitory neurotransmitter system in the brain, is the pharmacological target for many drugs used clinically to treat, for example, anxiety disorders and epilepsy, and to induce and maintain sedation, sleep, and anesthesia. These drugs facilitate the function of pentameric GABA(A) receptors that exhibit widespread expression in all brain regions and large structural and pharmacological heterogeneity as a result of composition from a repertoire of 19 subunit variants. One of the main problems in clinical use of GABA(A) receptor agonists is the development of tolerance. Most drugs, in long-term use and during withdrawal, have been associated with important modulations of the receptor subunit expression in brain-region-specific manner, participating in the mechanisms of tolerance and dependence. In most cases, the molecular mechanisms of regulation of subunit expression are poorly known, partly as a result of neurobiological adaptation to altered neuronal function. More knowledge has been obtained on the mechanisms of GABA(A) receptor trafficking and cell surface expression and the processes that may contribute to tolerance, although their possible pharmacological regulation is not known. Drug development for neuropsychiatric disorders, including epilepsy, alcoholism, schizophrenia, and anxiety, has been ongoing for several years. One key step to extend drug development related to GABA(A) receptors is likely to require deeper understanding of the adaptational mechanisms of neurons, receptors themselves with interacting proteins, and finally receptor subunits during drug action and in neuropsychiatric disease processes.

Ethanol action on dopaminergic neurons in the ventral tegmental area: interaction with intrinsic ion channels and neurotransmitter inputs

The dopaminergic system originating in the midbrain ventral tegmental area (VTA) has been extensively studied over the past decades as a critical neural substrate involved in the development of alcoholism and addiction to other drugs of abuse. Accumulating evidence indicates that ethanol modulates the functional output of this system by directly affecting the firing activity of VTA dopamine neurons, whereas withdrawal from chronic ethanol exposure leads to a reduction in the functional output of these neurons. This chapter will provide an update on the mechanistic investigations of the acute ethanol action on dopamine neuron activity and the neuroadaptations/plasticities in the VTA produced by previous ethanol experience.

The regulation of neuronal gene expression by alcohol

In recent years there has been an explosion of interest in how genes regulate alcohol drinking and contribute to alcoholism. This work has been stimulated by the completion of the human and mouse genome projects and the resulting availability of gene microarrays. Most of this work has been performed in drinking animals, and has utilized the extensive genetic variation among different mouse strains. At the same time, a much smaller amount of effort has gone into the in vitro study of the mechanisms underlying the regulation of individual genes by alcohol. These studies at the cellular and sub-cellular level are beginning to reveal the ways in which alcohol can interact with the transcriptional, translational and post-translational events inside the cell. Detailed studies of the promoter regions within several individual alcohol-responsive genes (ARGs) have been performed and this work has uncovered intricate signaling pathways that may be generalized to larger groups of ARGs. In the last few years several distinct ARGs have been identified from 35,000 mouse genes, by both the "top-down" approach (ex vivo gene arrays) and the "bottom-up" methods (in vitro promoter analysis). These divergent methodologies have converged on a surprisingly small number of genes encoding ion channels, receptors, transcription factors and proteins involved in synaptic function and remodeling. In this review we will describe some of the most interesting cellular and microarray work in the field, and will outline specific examples of genes for which the mechanisms of regulation by alcohol are now somewhat understood.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

Alcohol withdrawal-induced hippocampal neurotoxicity in vitro and seizures in vivo are both reduced by memantine

BACKGROUND

The ethanol withdrawal (EWD) syndrome is typically treated using benzodiazepines such as diazepam. However there is concern that benzodiazepines may not prevent neurotoxicity associated with EWD. Antagonists of glutamate/N-Methyl-D-Aspartate receptors (NMDARs) such as MK801 have been shown to be effective against both EWD-induced neurotoxicity in vitro and seizures in vivo. However, most of these agents have adverse side effects. An exception is the moderate affinity NMDAR channel blocker memantine, used in Alzheimer's dementia. The present studies examined the ability of memantine to protect against EWD-related toxicity in vitro and seizures in vivo.

METHODS

Organotypic hippocampal slice cultures from neonatal rat pups were treated starting at 15 days in vitro with 100 mM ethanol for 10 days followed by a 24-hour EWD period. During the 24-hour EWD period cultures were treated with memantine (15 or 30 microM). MK801 (10 microM) was utilized as a positive control. For the in vivo studies, the ability of memantine (2, 5, 10, and 15 mg/kg) to reduce convulsions was analyzed in Swiss-Webster mice using the handling induced convulsion test paradigm.

RESULTS

In vitro studies demonstrated that memantine is effective at blocking EWD-induced neurotoxicity. In vivo experiments showed that memantine also significantly reduced convulsions induced by EWD in mice.

CONCLUSIONS

Memantine may be of therapeutic value during alcohol detoxification by virtue of its having neuroprotective effects in addition to anti-seizure activity. The potential role of memantine in treatment of alcoholism is deserving of further study.

Phenobarbital withdrawal seizures may occur over several weeks before remitting: human data and hypothetical mechanism

This case is the first report of a patient who had phenobarbital (PB) withdrawal seizures after having been seizure-free for 3 years following temporal lobe surgery. The patient had been taking PB for 14 years when a gradual taper of PB was started. When PB was at 60 mg/d, a titration of lamotrigine (LTG) was started. However, typical complex seizures occurred when the patient was on PB 60 mg/d, along with LTG 25mg/d. PB was increased back to 90 mg/d and levetiracetam (LEV) was titrated. Seizures appeared when the patient was on PB 30 mg/d and LEV 750 mg BID and continued for 3 weeks after PB was stopped and the patient was on LEV 1,000 mg BID. For the following 6 months, her aura frequency remained elevated in comparison to her baseline aura of two auras per month for the previous year before the start of the PB taper. She was followed for 24 months after her last PB withdrawal seizure. During the last 8 months, her aura frequency returned to her baseline. As suggested by animal studies, the PB withdrawal seizures and increase in aura frequency in this patient may be explained by changes in her levels of GABA(A) receptor subunits.

Purinergic type 2 receptors at GABAergic synapses on ventral tegmental area dopamine neurons are targets for ethanol action

The current study investigated whether ethanol alters ATP activation of purinergic type 2 receptors (P2Rs) in the ventral tegmental area (VTA). The VTA is a key region of the brain that has been implicated in the development of alcohol addiction. We investigated the effects of ATP and ethanol on spontaneous inhibitory postsynaptic currents (sIPSCs) and the spontaneous firings in the VTA dopaminergic neurons, obtained using an enzyme-free procedure. These neurons preserved some functional GABA-releasing terminals after isolation. We found that ATP (1-200 microM) either increased or decreased the frequency of sIPSCs and the activity of VTA dopaminergic neurons. The effects of ATP on sIPSC frequency inversely correlated with its effects on dopaminergic neuron activity. The ATP-induced changes in sIPSC frequency were blocked by tetrodotoxin (a sodium channel blocker) and by suramin (a nonselective P2R antagonist). Furthermore, alpha,beta-methylene ATP, a selective P2X(1) and P2X(3) receptor agonist, increased sIPSC frequency, whereas adenosine 5'-[beta-thio]diphosphate, a preferential agonist of P2Y receptors, decreased sIPSC frequency. In experiments testing the effects of ethanol (10 and 40 mM) on sIPSCs, we found that ethanol significantly attenuated ATP-induced increase and enhanced ATP-induced decrease in sIPSC frequency. Taken together, the results demonstrate that multiple subtypes of P2Rs exist on GABA-releasing terminals that make synapses on VTA dopaminergic neurons. It seems that ATP increases sIPSC frequency involving P2X(1) and/or P2X(3) receptors, and ATP decreases sIPSC frequency involving P2YRs. These findings are also consistent with the notion that P2Rs at GABA-releasing terminals on VTA dopaminergic neurons are important targets for ethanol action.

Drug addiction as a pathology of staged neuroplasticity

Using addictive drugs can evolve from controlled social use into the compulsive relapsing disorder that characterizes addiction. This transition to addiction results from genetic, developmental, and sociological vulnerabilities, combined with pharmacologically induced plasticity in brain circuitry that strengthens learned drug-associated behaviors at the expense of adaptive responding for natural rewards. Advances over the last decade have identified the brain circuits most vulnerable to drug-induced changes, as well as many associated molecular and morphological underpinnings. This growing knowledge has contributed to an expanded understanding of how drugs usurp normal learning circuitry to create the pathology of addiction, as evidenced by involuntary activation of reward circuits in response to drug-associated cues and simultaneous reports of drug craving. This new understanding provides unprecedented potential opportunities for novel pharmacotherapeutic targets in treating addiction. There appears to be plasticity associated with the addiction phenomenon in general as well as changes produced by addiction to a specific class of addicting drugs. These findings also provide the basis for the current understanding of addiction as a chronic, relapsing disease of the brain with changes that persist long after the last use of the drug. Here, we describe the neuroplasticity in brain circuits and cell function induced by addictive drugs that is thought to underlie the compulsions to resume drug-taking, and discuss how this knowledge is impelling exploration and testing of novel addiction therapies.

Dopamine and benzodiazepine-dependent mechanisms regulate the EtOH-enhanced locomotor stimulation in the GABAA alpha1 subunit null mutant mice

The present study investigated the role of the alpha1-containing GABA(A) receptors in the neurobehavioral actions of alcohol. In Experiment 1, mice lacking the alpha1 subunit (alpha1 (-/-)) were tested for their capacity to initiate operant-lever press responding for alcohol or sucrose. Alcohol intake in the home cage was also measured. In Experiment 2, the alpha1 (-/-) mice were injected with a range of alcohol doses (0.875-4.0 g/kg; i.p.) to evaluate the significance of the alpha1 subunit in alcohol's stimulant actions. In Experiment 3, we determined if the alcohol-induced stimulant effects were regulated via dopaminergic (DA) or benzodiazepine (BDZ)-dependent mechanisms. To accomplish this, we investigated the capacity of DA (eticlopride, SCH 23390) and BDZ (flumazenil, betaCCt) receptor antagonists to attenuate the alcohol-induced stimulant actions. Compared with wild-type mice (alpha1 (+/+)), the null mutants showed marked reductions in both EtOH and sucrose-maintained responding, and home-cage alcohol drinking. The null mutants also showed significant increases in locomotor behaviors after injections of low-moderate alcohol doses (1.75-3.0 g/kg). betaCCt, flumazenil, eticlopride, and SCH 23390 were able to attenuate the alcohol-induced stimulation in mutant mice, in the absence of intrinsic effects. These data suggest the alpha1 receptor plays an important role in alcohol-motivated behaviors; however, it also appears crucial in regulating the reinforcing properties associated with normal ingestive behaviors. Deleting the alpha1 subunit of the GABA(A) receptor appears to unmask alcohol's stimulatory effects; these effects appear to be regulated via an interaction of both DA- and GABA(A) BDZ-dependent mechanisms.

Prenatal alcohol exposure alters GABA(A)alpha5 expression: a mechanism of alcohol-induced learning dysfunction

OBJECTIVE

In a model for fetal alcohol syndrome (FAS), we have previously found an alteration in NMDA receptors suggesting mediation, at least in part, of alcohol-related learning deficit. NMDA and GABA receptors interact in a multisynaptic circuit for the regulation of the inhibitory tone through the CNS. The GABA receptor subunit GABA(A)alpha5 is involved in learning and is developmentally regulated, as it is excitatory in the perinatal brain and inhibitory in the adult. We were interested to evaluate alcohol's effect on GABA(A)alpha5 expression to further understand alcohol-induced learning dysfunction.

STUDY DESIGN

Timed, pregnant C57B16/J mice were treated on gestational day 8 with alcohol (25% alcohol, 0.03 mL/kg i.p.) or control (saline). Embryos and brains were harvested 10 days after treatment, and brains from adult offspring were collected after evaluation in the Morris Water Maze, a well-established test for spatial learning. Gene expression included samples from at least 3 litters per timepoint, and calibrator-normalized relative real-time polymerase chain reaction (PCR) was performed to quantify GABA(A)alpha5 with GAPDH standardization. Statistical analysis included analysis of variance (ANOVA).

RESULTS

Prenatal alcohol exposure significantly decreased GABA(A)alpha5 expression in the embryo (P < .02) and fetal brains (P < .01) 10 days after therapy. However, in adult brains GABA(A)alpha5 expression was increased versus controls (P < .01). As previously demonstrated, prenatal alcohol exposure resulted in deficits in adults learning the Morris Water Maze with controls learning faster (P < .05).

CONCLUSION

Prenatal alcohol exposure alters developmental GABA(A)alpha5 expression. This may further explain the long-lasting damage of alcohol on learning skills. Both the alcohol-induced reduction in the GABA(A)alpha5 subunit during development and up-regulation in adult brain may be related to learning deficits resulting in decreased learning potential caused by the developmental defect and an increased inhibition of learning resulting from increased expression as an adult. In combination with our previous findings, these suggest that alcohol-induced learning impairment is likely the result of alterations of both NMDA and GABA expression and function.

Role of parvalbumin in estrogen protection from ethanol withdrawal syndrome

BACKGROUND

Parvalbumin (PA) is a calcium-binding protein that has been implicated in protecting neurons from hyperexcitability by sequestering intracellular calcium. This study examined whether ethanol exposure and/or ethanol withdrawal (EW) alter the levels of PA in a manner that is protected by 17beta-estradiol (E2).

METHODS

Ovariectomized rats implanted with E2 (EW/E2) or oil pellets (EW/Oil) received chronic ethanol (7.5% w/v, 5 weeks) or control dextrin (Dex/Oil and Dex/E2) diets. At 0 hr, 24 hr, and 2 weeks of EW, three brain areas (the cerebellum, hippocampus, and cortex) were prepared for immunoblotting and immunohistological assessment of PA.

RESULTS

At 24 hr of EW, the EW/Oil group showed reduced levels of PA protein and PA-positive neurons in the cerebellum and hippocampus compared with the dextrin control and the EW/E2 groups. At 2 weeks of EW, the reduced levels of PA persisted in the cerebellum but recovered toward the control levels in the hippocampus. The cortex showed no change in PA levels in any of the treatment groups. When tested at 24 hr of EW, the magnitude of EW signs inversely correlated with the levels of PA in the cerebellum and hippocampus. Ethanol exposure itself did not affect PA levels.

CONCLUSION

These data suggest that EW, rather than ethanol exposure, reduces PA levels in a manner that is brain region specific and that is protected by estrogen. Disturbed PA homeostasis is hypothesized to play a role in the hyperexcitability of EW signs.

Update on the neurobiology of alcohol withdrawal seizures

Abrupt cessation of alcohol intake after prolonged heavy drinking may trigger alcohol withdrawal seizures. Generalized tonic-clonic seizures are the most characteristic and severe type of seizure that occur in this setting. Generalized seizures also occur in rodent models of alcohol withdrawal. In these models, the withdrawal seizures are triggered by neuronal networks in the brainstem, including the inferior colliculus; similar brainstem mechanisms may contribute to alcohol withdrawal seizures in humans. Alcohol causes intoxication through effects on diverse ion channels and neurotransmitter receptors, including GABA(A) receptors--particularly those containing delta subunits that are localized extrasynaptically and mediate tonic inhibition--and N-methyl-D-aspartate (NMDA) receptors. Alcohol dependence results from compensatory changes during prolonged alcohol exposure, including internalization of GABA(A) receptors, which allows adaptation to these effects. Withdrawal seizures are believed to reflect unmasking of these changes and may also involve specific withdrawal-induced cellular events, such as rapid increases in alpha4 subunit-containing GABA(A) receptors that confer reduced inhibitory function. Optimizing approaches to the prevention of alcohol withdrawal seizures requires an understanding of the distinct neurobiologic mechanisms that underlie these seizures.

Role of GABAA alpha5-containing receptors in ethanol reward: the effects of targeted gene deletion, and a selective inverse agonist

GABA(A) receptors containing alpha5 subunits have been suggested to mediate the rewarding effects of ethanol. We tested this hypothesis in mice with deletion of alpha5 subunits. alpha5 knockout mice did not differ from wildtypes in operant responding for 10% ethanol/10% sucrose, but responded less for 10% sucrose. The benzodiazepine (BZ) site inverse agonist, Ro 15-4513, has higher affinity for GABA(A) receptors containing 5 subunits and dose-dependently (0-27 mg/kg, i.p.) reduced lever pressing for ethanol/sucrose in wildtype mice, but had less effect in knockout mice; lever pressing for sucrose was unaffected. These data suggest that alpha5 subunits are not essential for ethanol reward, but the reduction of operant responding for ethanol by Ro 15-4513 is mediated by alpha5-containing GABA(A) receptors. In measures of ethanol consumption, alpha5 knockout mice did not differ from wildtypes at low ethanol concentrations (2-8%), but consumed less ethanol at higher concentrations; these differences were not attributable to increased behavioural disruption of the knockout by ethanol, since no differences were seen in sensitivity to ethanol's sedative or ataxic effects. Ro 15-4513's ability to reduce ethanol consumption was unaffected, suggesting that this effect is not mediated by the alpha5 subtype. Secondly, we tested the ability of a novel alpha5-efficacy-selective benzodiazepine receptor ligand, alpha5IA-II, that possesses greater inverse agonist activity at alpha5- than at alpha1-, á2- or alpha3-containing GABA(A) receptors, to influence operant responding. alpha5IA-II (0.03-3 mg/kg) dose-dependently decreased lever pressing for 10% ethanol, the minimally effective dose of 1 mg/kg, corresponding to over 90% receptor occupancy, but did not affect lever pressing for 4% sucrose. Although inverse agonists acting at alpha5-containing receptors reduce ethanol self-administration, alpha5 subunits may not be essential to signaling ethanol reward.

Genetic basis for the psychostimulant effects of nicotine: a quantitative trait locus analysis in AcB/BcA recombinant congenic mice

Genetic differences in sensitivity to nicotine have been reported in both animals and humans. The present study utilized a novel methodology to map genes involved in regulating both the psychostimulant and depressant effects of nicotine in the AcB/BcA recombinant congenic strains (RCS) of mice. Locomotor activity was measured in a computerized open-field apparatus following subcutaneous administration of saline (days 1 and 2) or nicotine on day 3. The phenotypic measures obtained from this experimental design included total basal locomotor activity, as well as total nicotine activity, nicotine difference scores, nicotine percent change and nicotine regression residual scores. The results indicated that the C57BL/6J (B6) were insensitive to nicotine over the entire dose-response curve (0.1, 0.2, 0.4 and 0.8 mg/kg). However, the 0.8-mg/kg dose of nicotine produced a significant decrease in the locomotor activity in the A/J strain and a wide and continuous range of both locomotor excitation and depression among the AcB/BcA RCS. Single-locus association analysis in the AcB RCS identified quantitative trait loci (QTL) for the psychostimulant effects of nicotine on chromosomes 11, 12, 13, 14 and 17 and one QTL for nicotine-induced depression on chromosome 11. In the BcA RCS, nicotine-induced locomotor activation was associated with seven putative regions on chromosomes 2, 7, 8, 13, 14, 16 and 17. There were no overlapping QTL and no genetic correlations between saline- and nicotine-related phenotypes in the AcB/BcA RCS. A number of putative candidate genes were in proximity to regions identified with nicotine sensitivity, including the alpha2 subunit of the nicotinic acetylcholine receptor and the dopamine D3 receptor.

Glial cell line-derived neurotrophic factor mediates the desirable actions of the anti-addiction drug ibogaine against alcohol consumption

Alcohol addiction manifests as uncontrolled drinking despite negative consequences. Few medications are available to treat the disorder. Anecdotal reports suggest that ibogaine, a natural alkaloid, reverses behaviors associated with addiction including alcoholism; however, because of side effects, ibogaine is not used clinically. In this study, we first characterized the actions of ibogaine on ethanol self-administration in rodents. Ibogaine decreased ethanol intake by rats in two-bottle choice and operant self-administration paradigms. Ibogaine also reduced operant self-administration of ethanol in a relapse model. Next, we identified a molecular mechanism that mediates the desirable activities of ibogaine on ethanol intake. Microinjection of ibogaine into the ventral tegmental area (VTA), but not the substantia nigra, reduced self-administration of ethanol, and systemic administration of ibogaine increased the expression of glial cell line-derived neurotrophic factor (GDNF) in a midbrain region that includes the VTA. In dopaminergic neuron-like SHSY5Y cells, ibogaine treatment upregulated the GDNF pathway as indicated by increases in phosphorylation of the GDNF receptor, Ret, and the downstream kinase, ERK1 (extracellular signal-regulated kinase 1). Finally, the ibogaine-mediated decrease in ethanol self-administration was mimicked by intra-VTA microinjection of GDNF and was reduced by intra-VTA delivery of anti-GDNF neutralizing antibodies. Together, these results suggest that GDNF in the VTA mediates the action of ibogaine on ethanol consumption. These findings highlight the importance of GDNF as a new target for drug development for alcoholism that may mimic the effect of ibogaine against alcohol consumption but avoid the negative side effects.

Role of the GABA-A system in estrogen-induced protection against brain lipid peroxidation in ethanol-withdrawn rats

BACKGROUND

Our previous study showed that 17 beta-estradiol (E2) treatment protects against cerebellar neuronal death and related motor deficits in ethanol-withdrawn rats, in part through the GABAergic system. In this study, we examined the effect of the GABA-A antagonist bicuculline on the neuroprotective effect of E2 by assessing the oxidative marker thiobarbituric acid reactive substances (TBARS) during ethanol withdrawal (EW).

METHODS

Ovariectomized animals that had implants of E2 (EW/E2) or oil (EW/Oil) pellets received liquid ethanol (7.5% w/v) or dextrin for 7 days by gavage. The GABA-A antagonist bicuculline (1.25 mg/kg) was administered (three times a day intraperitoneally) for 4 days starting 3 days before the onset of EW. After testing for overt EW signs at 7 hr of EW, one set of the animals was immediately killed for the collection of the cerebellum, hippocampus, and cortex. The brain homogenates were further processed for TBARS assay to detect TBARS in the presence or absence of FeCl(3). For assessing motor capacity, the other set of animals was tested for the latency to fall from a rotarod after 1 week of EW.

RESULTS

The EW/Oil animals had enhanced endogenous and FeCl(3)-stimulated TBARS levels in the cerebellum and the hippocampus in a manner potentiated by bicuculline but inhibited by E2. Bicuculline counteracted the protective effect of E2 when administered along with E2. Pearson correlation coefficients indicated that the latency to fall from the rotarod covaried with TBARS levels in the cerebellum and the hippocampus.

CONCLUSION

These data suggest that E2 protects against lipid peroxidation in vulnerable brain areas of ethanol-withdrawn rats, in part through the GABAergic system.

Effect of chronic administration of ethanol on GABAA receptor assemblies derived from α2-, α3-, β2- and γ2-subunits in the rat cerebral cortex

Chronic administration of ethanol decreased the immunoprecipitation of the [(3)H]flunitrazepam binding activity for GABA(A) receptor assemblies derived from alpha(2)-, alpha(3)- and gamma(2)-subunits in the rat cerebral cortex. However, the [(3)H]muscimol binding sites derived from these subunits were not affected. Thus, chronic ethanol causes the down-regulation of the benzodiazepine sites derived from the alpha(2)-, alpha(3)- and gamma(2)-subunits without affecting the GABA binding sites.

GABAA receptor β subunit mRNA expression in the human alcoholic brain

A competitive RT-PCR assay was used to quantify the expression of the GABA(A) receptor beta(1), beta(2) and beta(3) isoform mRNA transcripts in the superior frontal cortex and motor cortex of 21 control and 22 alcoholic cases. A single set of primers was designed that permitted amplification of all three transcripts and the internal standard simultaneously; differentiation of the individual transcripts was achieved by restriction enzyme digestion. Construction of a standard curve, using the internal standard and a concentration range of beta(2) cRNA-enabled quantitation of mRNA expression levels. No significant difference in mRNA expression was found between the control and alcoholic case groups in either the superior frontal or motor cortex for the beta(2) or beta(3) isoforms. A significant interaction was found between isoform and area, although, the two case groups did not partition on this measure. The interaction was due to a significant difference between superior frontal and motor cortex for the beta(3) isoform; this regional comparison was not significant for beta(2) mRNA. Age at death and post-mortem delay (PMD) had no significant effect on beta mRNA expression in either case group in either region. A beta(1) signal could not be detected in the RT-PCR assay.

Estrogen protects against brain lipid peroxidation in ethanol-withdrawn rats

This study examined whether 17beta-estradiol (E2) administration protects against ethanol withdrawal (EW)-associated oxidative insults by assessing oxidative markers thiobarbituric-acid-reacting-substances (TBARS). Ovariectomized rats implanted with E2 (EW/E2) or oil pellets (EW/Oil) received chronic ethanol (7.5% wt./vol., 5 weeks) or control dextrin diet (Dextrin/Oil). At 24 or 48 h of EW, rats were tested for overt EW signs and the cerebellum, hippocampus, and cortex were prepared for TBARS assessment in the presence and absence of FeCl3. For control experiments, we assessed E2 effects on blood ethanol concentrations and TBARS levels during ethanol exposure prior to EW. The EW/Oil group showed enhanced endogenous- and FeCl3-stimulated membrane TBARS levels in the cerebellum and hippocampus in a manner inhibited by E2 treatment. There was a relationship between the severity of EW and elevation of TBARS levels, particularly in the cerebellum. The enhanced TBARS levels at 24 h of EW appeared to diminish at 48 h in the hippocampus, but persisted in the cerebellum. E2 treatment did not alter blood ethanol concentrations and ethanol exposure alone did not enhance TBARS levels. These data suggest that EW rather than ethanol enhances brain lipid peroxidation that is transient and brain-region specific. Estrogens protect against the brain lipid peroxidation in a manner independent of blood ethanol concentrations.

Differential effects of chronic ethanol administration and withdrawal on gamma-aminobutyric acid type A and NMDA receptor subunit proteins in male and female rat brain

BACKGROUND

Investigations have shown that chronic ethanol exposure results in selective alterations in levels of gamma-aminobutyric acid (GABA)A and NMDA receptor subunits. We previously reported significant sex differences in these chronic ethanol-induced adaptations. Because we have more recently found important sex differences in timing for the development of and recovery from ethanol dependence, we wanted to ascertain whether there were associations between overt expression of withdrawal and neuroadaptations at the level of GABAA and NMDA receptors.

METHODS

Western blot analysis was used to assay protein levels for several GABAA and NMDA receptor subunits in rat cerebral cortex and hippocampus by using subunit-selective antibodies. Rats were fed 6% ethanol in a liquid diet with pair-fed controls. Feeding, harvesting of tissue, and Western blot experiments were all conducted while maintaining the paired design. Tissue was harvested after 3 days of ethanol exposure, 9 days of ethanol exposure, or 3 days of ethanol withdrawal after 14 days of liquid diet administration.

RESULTS

We again found sex-, subunit-, and brain region-selective effects of ethanol administration and withdrawal for GABAA and NMDA receptors. There was a strong association between increased GABAA receptor alpha4 subunit levels and previously determined withdrawal-induced changes in seizure susceptibility, highlighted by the sex differences in ethanol exposure length required to cause withdrawal signs. In addition, results obtained after 9 days of ethanol administration were in general agreement with previous findings after 14 days of ethanol administration.

CONCLUSIONS

These data further support the suggestion that alterations in subunit assembly of GABAA and NMDA receptors may have some mechanistic role in neuroadaptations underlying ethanol dependence and withdrawal. Furthermore, significant sex differences in these adaptations suggest that multiple types of adaptations may be elicited, depending on innate differences in the actions/effects of ethanol.