Long-term ethanol self-administration by cynomolgus macaques alters the pharmacology and expression of GABAA receptors in basolateral amygdala

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.

Sex differences in stress-induced alcohol intake: a review of preclinical studies focused on amygdala and inflammatory pathways

Clinical studies suggest that women are more likely than men to relapse to alcohol drinking in response to stress; however, the mechanisms underlying this sex difference are not well understood. A number of preclinical behavioral models have been used to study stress-induced alcohol intake. Here, we review paradigms used to study effects of stress on alcohol intake in rodents, focusing on findings relevant to sex differences. To date, studies of sex differences in stress-induced alcohol drinking have been somewhat limited; however, there is evidence that amygdala-centered circuits contribute to effects of stress on alcohol seeking. In addition, we present an overview of inflammatory pathways leading to microglial activation that may contribute to alcohol-dependent behaviors. We propose that sex differences in neuronal function and inflammatory signaling in circuits centered on the amygdala are involved in sex-dependent effects on stress-induced alcohol seeking and suggest that this is an important area for future studies.

Rich Club Characteristics of Alcohol-Naïve Functional Brain Networks Predict Future Drinking Phenotypes in Rhesus Macaques

Purpose: A fundamental question for Alcohol use disorder (AUD) is how and when naïve brain networks are reorganized in response to alcohol consumption. The current study aimed to determine the progression of alcohol’s effect on functional brain networks during transition from the naïve state to chronic consumption.

Procedures: Resting-state brain networks of six female rhesus macaque (Macaca mulatta) monkeys were acquired using magnetoencephalography (MEG) prior to alcohol exposure and after free-access to alcohol using a well-established model of chronic heavy alcohol consumption. Functional brain network metrics were derived at each time point.

Results: The average connection frequency (p < 0.024) and membership of the Rich Club (p < 0.022) changed significantly over time. Metrics describing network topology remained relatively stable from baseline to free-access drinking. The minimum degree of the Rich Club prior to alcohol exposure was significantly predictive of future free-access drinking (r = −0.88, p < 0.001).

Conclusions: Results suggest naïve brain network characteristics may be used to predict future alcohol consumption, and that alcohol consumption alters functional brain networks, shifting hubs and Rich Club membership away from previous regions in a non-systematic manner. Further work to refine these relationships may lead to the identification of a high-risk drinking phenotype.

Regulation of GABAA Receptor Subunit Expression in Substance Use Disorders

The modulation of neuronal cell firing is mediated by the release of the neurotransmitter GABA (γ-aminobuytric acid), which binds to two major families of receptors. The ionotropic GABAA receptors (GABA_ARs) are composed of five distinct subunits that vary in expression by brain region and cell type. The action of GABA on GABA_ARs is modulated by a variety of clinically and pharmacologically important drugs such as benzodiazepines and alcohol. Exposure to and abuse of these substances disrupts homeostasis and induces plasticity in GABAergic neurotransmission, often via the regulation of receptor expression. Here, we review the regulation of GABA_AR subunit expression in adaptive and pathological plasticity, with a focus on substance use. We examine the factors influencing the expression of GABA_AR subunit genes including the regulation of the 5′ and 3′ untranslated regions, variations in DNA methylation, immediate early genes and transcription factors that regulate subunit expression, translational and post-translational modifications, and other forms of receptor regulation beyond expression. Advancing our understanding of the factors regulating GABA_AR subunit expression during adaptive plasticity, as well as during substance use and withdrawal will provide insight into the role of GABAergic signaling in substance use disorders, and contribute to the development of novel targeted therapies.

GABAA Receptor Subtypes and the Abuse-Related Effects of Ethanol in Rhesus Monkeys: Experiments with Selective Positive Allosteric Modulators

BACKGROUND

Previous studies have investigated α1GABAA and α5GABAA receptor mechanisms in the behavioral effects of ethanol (EtOH) in monkeys. However, genetic studies in humans and preclinical studies with mutant mice suggest a role for α2GABAA and/or α3GABAA receptors in the effects of EtOH. The development of novel positive allosteric modulators (PAMs) with functional selectivity (i.e., selective efficacy) at α2GABAA and α3GABAA receptors allows for probing of these subtypes in preclinical models of the discriminative stimulus and reinforcing effects of EtOH in rhesus macaques.

METHODS

In discrimination studies, subjects were trained to discriminate EtOH (2 g/kg, intragastrically) from water under a fixed-ratio (FR) schedule of food delivery. In oral self-administration studies, subjects were trained to self-administer EtOH (2% w/v) or sucrose (0.3 to 1% w/v) under an FR schedule of solution availability.

RESULTS

In discrimination studies, functionally selective PAMs at α2GABAA and α3GABAA (HZ-166) or α3GABAA (YT-III-31) receptors substituted fully (maximum percentage of EtOH-lever responding ≥80%) for the discriminative stimulus effects of EtOH without altering response rates. Full substitution for EtOH also was engendered by a nonselective PAM (triazolam), an α5GABAA -preferring PAM (QH-ii-066) and a PAM at α2GABAA , α3GABAA , and α5GABAA receptors (L-838417). A partial (MRK-696) or an α1GABAA -preferring (zolpidem) PAM only engendered partial substitution (i.e., ~50 to 60% EtOH-lever responding). In self-administration studies, pretreatments with the functionally selective PAMs at α2GABAA and α3GABAA (XHe-II-053 and HZ-166) or α3GABAA (YT-III-31 and YT-III-271) receptors increased EtOH, but not sucrose, drinking at doses that had few, or no, observable sedative-motor effects.

CONCLUSIONS

Our results confirm prior findings regarding the respective roles of α1GABAA and α5GABAA receptors in the discriminative stimulus effects of EtOH and, further, suggest a key facilitatory role for α3GABAA and potentially α2GABAA receptors in several abuse-related effects of EtOH in monkeys. Moreover, they reveal a potential role for these latter subtypes in EtOH's sedative effects.

Ethanol withdrawal limits fear memory reactivation-induced molecular events associated with destabilization phase: Influence of d-cycloserine

A 1-day fear memory in ethanol withdrawn (ETOH) rats is resistant to destabilization-reconsolidation process. However, d-cycloserine (DCS) reverts this disturbance. Considering that the formation of pathological fear memories in humans often occurs long time before the requirement of an intervention, the study of older memories is relevant in ETOH rats. In addition, the resistance to destabilization and DCS effect on this memory phase at molecular level in ETOH rats have not been corroborated yet. Firstly, we examined the effect of a pharmacological intervention after reactivation on reconsolidation of a 7-day fear memory in ETOH rats. Then, and considering that enhanced GluN2B expression and ubiquitin-proteasome system (UPS) activity are involved in destabilization, we evaluated them following reactivation in ETOH rats. Furthermore, DCS effect on such destabilization markers was examined. It was found that the pharmacological intervention after reactivation did not affect the 7-day fear memory in ETOH rats with DCS reversing this resistance. Memory reactivation increased GluN2B expression, polyubiquitination levels and proteasome activity in the basolateral amygdala complex (BLA) of control (CON) rats only; without affecting these molecular events in ETOH rats. Finally, ETOH rats treated with DCS and CON animals displayed elevated and similar UPS activities in the BLA after reactivation. In conclusion, the reactivation of an older fear memory formed during ethanol withdrawal does not trigger the molecular events associated with destabilization, and DCS facilitates this memory phase by enhancing the UPS activity.

GABA and Glutamate Synaptic Coadaptations to Chronic Ethanol in the Striatum

Alcohol (ethanol) is a widely used and abused drug with approximately 90% of adults over the age of 18 consuming alcohol at some point in their lifetime. Alcohol exerts its actions through multiple neurotransmitter systems within the brain, most notably the GABAergic and glutamatergic systems. Alcohol's actions on GABAergic and glutamatergic neurotransmission have been suggested to underlie the acute behavioral effects of ethanol. The striatum is the primary input nucleus of the basal ganglia that plays a role in motor and reward systems. The effect of ethanol on GABAergic and glutamatergic neurotransmission within striatal circuitry has been thought to underlie ethanol taking, seeking, withdrawal and relapse. This chapter reviews the effects of ethanol on GABAergic and glutamatergic transmission, highlighting the dynamic changes in striatal circuitry from acute to chronic exposure and withdrawal.

Neuroactive Steroid (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP) and Pro-inflammatory Cytokine MCP-1 Levels in Hippocampus CA1 are Correlated with Voluntary Ethanol Consumption in Cynomolgus Monkey

BACKGROUND

Neuroactive steroids such as (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP, allopregnanolone) are potent neuromodulators that enhance GABAergic neurotransmission and produce inhibitory neurobehavioral and anti-inflammatory effects. Chronic ethanol (EtOH) consumption reduces 3α,5α-THP levels in human plasma, but has brain region- and species-specific effects on central nervous system levels of 3α,5α-THP. We explored the relationship between 3α,5α-THP levels in the hippocampus and voluntary EtOH consumption in the cynomolgus monkey following daily self-administration of EtOH for 12 months and further examined the relationship with hypothalamic-pituitary-adrenal (HPA) axis function prior to EtOH exposure. We simultaneously explored hippocampus levels of monocyte chemoattractant protein 1 (MCP-1), a pro-inflammatory cytokine that plays an important role in the neuroimmune response to EtOH, following chronic self-administration.

METHODS

Monkeys were subjected to scheduled induction of water and EtOH consumption (0 to 1.5 g/kg) over 4 months, followed by free access to EtOH or water for 22 h/d over 12 months. Immunohistochemistry was performed using an anti-3α,5α-THP or anti-MCP-1 antibody. Prolonged voluntary drinking resulted in individual differences in EtOH consumption that ranged from 1.2 to 4.2 g/kg/d over 12 months.

RESULTS

Prolonged EtOH consumption increased cellular 3α,5α-THP immunoreactivity by 12 ± 2% (p < 0.05) and reduced MCP-1 immunoreactivity by 23 ± 9% (p < 0.05) in the hippocampus CA1. In both cases, the effect of EtOH was most pronounced in heavy drinkers that consumed ≥3 g/kg for ≥20% of days. 3α,5α-THP immunoreactivity was positively correlated with average daily EtOH intake (Spearman r = 0.76, p < 0.05) and dexamethasone inhibition of HPA axis function (Spearman r = 0.9, p < 0.05). In contrast, MCP-1 immunoreactivity was negatively correlated with average daily EtOH intake (Spearman r = -0.78, p < 0.05) and dexamethasone suppression of HPA axis function (Spearman r = -0.76, p < 0.05). Finally, 3α,5α-THP and MCP-1 immunoreactivity were inversely correlated with each other (Spearman r = -0.68, p < 0.05).

CONCLUSIONS

These data indicate that voluntary, long-term EtOH consumption results in higher levels of 3α,5α-THP, while decreasing levels of MCP-1 in the CA1 hippocampus, and that both changes may be linked to HPA axis function and the magnitude of voluntary EtOH consumption.

Changes in nonhuman primate brain function following chronic alcohol consumption in previously naïve animals

INTRODUCTION

Chronic alcohol abuse is associated with neurophysiological changes in brain activity; however, these changes are not well localized in humans. Non-human primate models of alcohol abuse enable control over many potential confounding variables associated with human studies. The present study utilized high-resolution magnetoencephalography (MEG) to quantify the effects of chronic EtOH self-administration on resting state (RS) brain function in vervet monkeys.

METHODS

Adolescent male vervet monkeys were trained to self-administer ethanol (n=7) or an isocaloric malto-dextrin solution (n=3). Following training, animals received 12 months of free access to ethanol. Animals then underwent RS magnetoencephalography (MEG) and subsequent power spectral analysis of brain activity at 32 bilateral regions of interest associated with the chronic effects of alcohol use.

RESULTS

demonstrate localized changes in brain activity in chronic heavy drinkers, including reduced power in the anterior cingulate cortex, hippocampus, and amygdala as well as increased power in the right medial orbital and parietal areas.

DISCUSSION

The current study is the first demonstration of whole-head MEG acquisition in vervet monkeys. Changes in brain activity were consistent with human electroencephalographic studies; however, MEG was able to extend these findings by localizing the observed changes in power to specific brain regions. These regions are consistent with those previously found to exhibit volume loss following chronic heavy alcohol use. The ability to use MEG to evaluate changes in brain activity following chronic ethanol exposure provides a potentially powerful tool to better understand both the acute and chronic effects of alcohol on brain function.

Voluntary ethanol consumption reduces GABAergic neuroactive steroid (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP) in the amygdala of the cynomolgus monkey

Neuroactive steroids such as (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP, allopregnanolone) enhance the gamma-aminobutyric acid (GABA)-ergic effects of ethanol and modulate excessive drinking in rodents. Moreover, chronic ethanol consumption reduces 3α,5α-THP levels in human plasma, rat hippocampus and mouse limbic regions. We explored the relationship between 3α,5α-THP levels in limbic brain areas and voluntary ethanol consumption in the cynomolgus monkey following daily self-administration of ethanol for 12 months and further examined the relationship to hypothalamic-pituitary-adrenal (HPA) axis function prior to ethanol exposure. Monkeys were subjected to scheduled induction of ethanol consumption followed by free access to ethanol or water for 22 h/day over 12 months. Immunohistochemistry was performed using an anti-3α,5α-THP antibody. Prolonged voluntary drinking resulted in individual differences in ethanol consumption that ranged from 1.2 to 4.2 g/kg/day over 12 months. Prolonged ethanol consumption reduced cellular 3α,5α-THP immunoreactivity by 13 ± 2 percent (P < 0.05) in the lateral amygdala and 17 ± 2 percent (P < 0.05) in the basolateral amygdala. The effect of ethanol was most pronounced in heavy drinkers that consumed ≥3 g/kg ≥ 20 percent of days. Consequently, 3α,5α-THP immunoreactivity in both the lateral and basolateral amygdala was inversely correlated with average daily ethanol intake (Spearman r = -0.87 and -0.72, respectively, P < 0.05). However, no effect of ethanol and no correlation between drinking and 3α,5α-THP immunoreactivity were observed in the basomedial amygdala. 3α,5α-THP immunoreactivity following ethanol exposure was also correlated with HPA axis function prior to ethanol exposure. These data indicate that voluntary ethanol drinking reduces amygdala levels of 3α,5α-THP in non-human primates and that amygdala 3α,5α-THP levels may be linked to HPA axis function.

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".

The effect of Midazolam and Propranolol on fear memory reconsolidation in ethanol-withdrawn rats: influence of d-cycloserine

BACKGROUND

Withdrawal from chronic ethanol facilitates the formation of contextual fear memory and delays the onset to extinction, with its retrieval promoting an increase in ethanol consumption. Consequently, manipulations aimed to reduce these aversive memories, may be beneficial in the treatment of alcohol discontinuation symptoms. Related to this, pharmacological memory reconsolidation blockade has received greater attention due to its therapeutic potential.

METHODS

Here, we examined the effect of post-reactivation amnestic treatments such as Midazolam (MDZ, 3 mg/kg i.p) and Propranolol (PROP, 5 mg/kg i.p) on contextual fear memory reconsolidation in ethanol- withdrawn (ETOH) rats. Next, we examined whether the activation of N-methyl-D-aspartate (NMDA) receptors induced by d-cycloserine (DCS, 5 mg/kg i.p., a NMDA partial agonist) before memory reactivation can facilitate the disruptive effect of PROP and MDZ on fear memory in ETOH rats.

RESULTS

We observed a resistance to the disruptive effect of both MDZ and PROP following memory reactivation. Although intra-basolateral amygdala (BLA; 1.25 ug/side) and systemic PROP administration attenuated fear memory in DCS pre-treated ETOH rats, DCS/MDZ treatment did not affect memory in these animals. Finally, a decrease of both total and surface protein expression of the α1 GABAA receptor (GABAA-R) subunit in BLA was found in the ETOH rats.

CONCLUSIONS

Ethanol withdrawal facilitated the formation of fear memory resistant to labilization post-reactivation. DCS administration promoted the disruptive effect of PROP on memory reconsolidation in ETOH rats. The resistance to MDZ's disruptive effect on fear memory reconsolidation may be, at least in part, associated with changes in the GABAA-R composition induced by chronic ethanol administration/withdrawal.

Monkey alcohol tissue research resource: banking tissues for alcohol research

BACKGROUND

An estimated 18 million adults in the United States meet the clinical criteria for diagnosis of alcohol abuse or alcoholism, a disorder ranked as the third leading cause of preventable death. In addition to brain pathology, heavy alcohol consumption is comorbid with damage to major organs including heart, lungs, liver, pancreas, and kidneys. Much of what is known about risk for and consequences of heavy consumption derive from rodent or retrospective human studies. The neurobiological effects of chronic intake in rodent studies may not easily translate to humans due to key differences in brain structure and organization between species, including a lack of higher-order cognitive functions, and differences in underlying prefrontal cortical neural structures that characterize the primate brain. Further, rodents do not voluntarily consume large quantities of ethanol (EtOH) and they metabolize it more rapidly than primates.

METHODS

The basis of the Monkey Alcohol Tissue Research Resource (MATRR) is that nonhuman primates, specifically monkeys, show a range of drinking excessive amounts of alcohol (>3.0 g/kg or a 12 drink equivalent per day) over long periods of time (12 to 30 months) with concomitant pathological changes in endocrine, hepatic, and central nervous system (CNS) processes. The patterns and range of alcohol intake that monkeys voluntarily consume parallel what is observed in humans with alcohol use disorders and the longitudinal experimental design spans stages of drinking from the EtOH-naïve state to early exposure through chronic abuse. Age- and sex-matched control animals self-administer an isocaloric solution under identical operant procedures.

RESULTS

The MATRR is a unique postmortem tissue bank that provides CNS and peripheral tissues, and associated bioinformatics from monkeys that self-administer EtOH using a standardized experimental paradigm to the broader alcohol research community.

CONCLUSIONS

This resource provides a translational platform from which we can better understand the disease processes associated with alcoholism.

Ethanol-induced plasticity of GABAA receptors in the basolateral amygdala

Acute and chronic ethanol (EtOH) administration is known to affect function, surface expression, and subunit composition of γ-aminobutyric acid (A) receptors (GABAARs) in different parts of the brain, which is believed to play a major role in alcohol dependence and withdrawal symptoms. The basolateral amygdala (BLA) participates in anxiety-like behaviors including those induced by alcohol withdrawal. In the present study we assessed the changes in cell surface levels of select GABAAR subunits in the BLA of a rat model of alcohol dependence induced by chronic intermittent EtOH (CIE) treatment and long-term (>40 days) withdrawal and investigated the time-course of such changes after a single dose of EtOH (5 g/kg, gavage). We found an early decrease in surface expression of α4 and δ subunits at 1 h following single dose EtOH treatment. At 48 h post-EtOH and after CIE treatment there was an increase in α4 and γ2, while α1, α2, and δ surface expression were decreased. To relate functional changes in GABAARs to changes in their subunit composition we analyzed miniature inhibitory postsynaptic currents (mIPSCs) and the picrotoxin-sensitive tonic current (Itonic) 48 h after EtOH intoxication. The Itonic magnitude and most of the mIPSC kinetic parameters (except faster mIPSC decay) were unchanged at 48 h post-EtOH. At the same time, Itonic potentiation by acute EtOH was greatly reduced, whereas mIPSCs became significantly more sensitive to potentiation by acute EtOH. These results suggest that EtOH intoxication-induced GABAAR plasticity in the BLA might contribute to the diminished sedative/hypnotic and maintained anxiolytic effectiveness of EtOH.

Little evidence of a role for the α1GABAA subunit-containing receptor in a rhesus monkey model of alcohol drinking

BACKGROUND

Alcohol potentiates GABAergic neurotransmission via action at the GABAA receptor. α1 subunit-containing GABAA receptors have been implicated as mediators, in part, of the behavioral and abuse-related effects of alcohol in rodents.

METHODS

We systematically investigated the effects of 1 α1-preferring benzodiazepine agonist, zolpidem, and 2 antagonists, β-carboline-3-carboxylate-tert-butyl ester (βCCT) and 3-propoxy-β-carboline hydrochloride (3-PBC), on oral self-administration of alcohol (2% w/v) or sucrose solution and observable behavior in rhesus macaques. We compared these effects to those of the nonselective benzodiazepine agonist triazolam, antagonist flumazenil, and inverse agonist β-carboline carboxylate (βCCE).

RESULTS

Alcohol and sucrose solutions maintained reliable baseline drinking behavior across the study. The α1-preferring compounds did not affect intake, number of sipper extensions, or blood alcohol levels (BALs) at any of the doses tested. Zolpidem, βCCT, and 3-PBC increased latency to first sipper extension in animals self-administering alcohol, but not sucrose, solution. Triazolam exerted biphasic effects on alcohol-drinking behavior, increasing intake at low doses but decreasing BAL and increasing latency at higher doses. At doses higher than those effective in alcohol-drinking animals, triazolam increased sucrose intake and latency. Flumazenil nonsystematically increased number of extensions for alcohol but decreased BAL, with no effects on sucrose drinking. βCCE decreased sipper extensions for alcohol and increased latency for first sucrose sipper extension, but full dose-effect relationships could not be determined due to seizures at higher doses.

CONCLUSIONS

Alcohol-drinking animals appeared more sensitive to the effects of GABAergic compounds on drinking behavior. However, these results do not support a strong contribution of α1GABAA receptors to the reinforcing effects of alcohol in primates.

Standardized method for the harvest of nonhuman primate tissue optimized for multiple modes of analyses

Appropriate animal models are critical to conduct translational studies of human disorders without variables that can confound clinical studies. Such analytic methods as patch-clamp electrophysiological and voltammetric recordings of neurons in brain slices require living brain tissue. In order to obtain viable tissue from nonhuman primate brains, tissue collection methods must be designed to preserve cardiovascular and respiratory functions for as long as possible. This paper describes a method of necropsy that has been used in three species of monkeys that satisfies this requirement. At necropsy, animals were maintained under a deep surgical plane of anesthesia while a craniotomy was conducted to expose the brain. Following the craniotomy, animals were perfused with ice-cold, oxygenated artificial cerebrospinal fluid to displace blood and to reduce the temperature of the entire brain. The brain was removed within minutes of death and specific brain regions were immediately dissected for subsequent in vitro electrophysiology or voltammetry experiments. This necropsy method also provided for the collection of tissue blocks containing all brain regions that were immediately frozen and stored for subsequent genomic, proteomic, autoradiographic and histological studies. An added benefit from the design of this necropsy method is that all major peripheral tissues were also collected and are now being utilized in a wide range of genomic, biochemical and histological assays. This necropsy method has resulted in the establishment and growth of a nonhuman primate alcohol tissue bank designed to distribute central nervous system and peripheral tissues to the larger scientific community.

Effects of the benzodiazepine GABAA α1-preferring ligand, 3-propoxy-β-carboline hydrochloride (3-PBC), on alcohol seeking and self-administration in baboons

RATIONALE

The various α subtypes of GABAA receptors have been strongly implicated in alcohol reinforcement and consumption.

OBJECTIVES

The effects of the GABAA α1-preferring ligand, 3-propoxy-β-carboline hydrochloride (3-PBC), on seeking and self-administration responses were evaluated in two groups of baboons trained under a 3-component chained schedule of reinforcement (CSR).

METHODS

Alcohol (4 % w/v; n = 5; alcohol group) or a preferred nonalcoholic beverage (n = 4; control group) was available for self-administration only in component 3 of the CSR. Responses in component 2 provided indices of motivation to drink (seeking). 3-PBC (1.0-30.0 mg/kg) and saline were administered before drinking sessions under both acute and 5-day dosing conditions.

RESULTS

Repeated, and not acute, doses of 3-PBC significantly decreased total self-administration responses (p < 0.05), volume consumed (p < 0.05), and gram per kilogram of alcohol (p < 0.05) in the alcohol group. In the control group, 5-day administration of 3-PBC significantly decreased total self-administration responses (p < 0.05) but produced nonsignificant decreases in volume consumed. Within-session pattern of drinking was characterized by a high level of drinking in the first 20 min of the session for both groups, which was significantly (p < 0.05) decreased by all doses of 3-PBC (1.0-18.0 mg/kg) only in the alcohol group. In contrast, the first drinking bout in the control group was only reduced at the highest doses of 3-PBC (10.0 and 18.0 mg/kg).

CONCLUSIONS

The results support the involvement of the GABAA α1 subtype receptor in alcohol reinforcement and consumption.

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.

Neuropeptide modulation of central amygdala neuroplasticity is a key mediator of alcohol dependence

Alcohol use disorders are characterized by compulsive drug-seeking and drug-taking, loss of control in limiting intake, and withdrawal syndrome in the absence of drug. The central amygdala (CeA) and neighboring regions (extended amygdala) mediate alcohol-related behaviors and chronic alcohol-induced plasticity. Acute alcohol suppresses excitatory (glutamatergic) transmission whereas chronic alcohol enhances glutamatergic transmission in CeA. Acute alcohol facilitates inhibitory (GABAergic) transmission in CeA, and chronic alcohol increases GABAergic transmission. Electrophysiology techniques are used to explore the effects of neuropeptides/neuromodulators (CRF, NPY, nociceptin, dynorphin, endocannabinoids, galanin) on inhibitory transmission in CeA. In general, pro-anxiety peptides increase, and anti-anxiety peptides decrease CeA GABAergic transmission. These neuropeptides facilitate or block the action of acute alcohol in CeA, and chronic alcohol produces plasticity in neuropeptide systems, possibly reflecting recruitment of negative reinforcement mechanisms during the transition to alcohol dependence. A disinhibition model of CeA output is discussed in the context of alcohol dependence- and anxiety-related behaviors.

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'.

Chronic ethanol and withdrawal differentially modulate lateral/basolateral amygdala paracapsular and local GABAergic synapses

Withdrawal-related anxiety is cited as a major contributor to relapse in recovering alcoholics. Changes in lateral/basolateral amygdala (BLA) neurotransmission could directly influence anxiety-like behaviors after chronic ethanol exposure and withdrawal. We have shown that these treatments enhance BLA glutamatergic function and neurotransmission. However, the BLA GABAergic system tightly controls the expression of anxiety-like behavior, and additional neuroadaptations in this system are potentially important as well. The intrinsic BLA GABAergic system consists of at least two populations of interneurons: local feed-back interneurons scattered throughout the region and feed-forward interneurons concentrated within groups found in the lateral/paracapsular region of the BLA. In the present study, we found that withdrawal from chronic ethanol robustly decreased presynaptic function at feed-forward GABA synapses but did not alter neurotransmitter release from local interneurons. Differential presynaptic changes at these synapses were complemented by decreased zolpidem sensitivity at feed-forward synapses and decreased midazolam sensitivity at local synapses. Consistent with this, chronic ethanol/withdrawal decreased expression of GABA α1-subunit total protein and increased surface expression of α4-subunit protein. We also found transient increases in GABA-receptor-associated protein levels and persistent increases in γ2-subunit and gephyrin proteins that would suggest alterations in GABA(A) receptor trafficking that might help regulate changes in α4-subunit localization. These data together suggest that chronic ethanol and withdrawal differentially modulate local and lateral paracapsular cell GABAergic synapses via distinct presynaptic and postsynaptic mechanisms. These findings extend our understanding of the neurobiological mechanisms governing changes in anxiety-like behavior after chronic ethanol exposure and withdrawal.

Classification of alcohol abuse by plasma protein biomarkers

BACKGROUND

Biochemical diagnostics of ethanol intake would improve alcohol abuse treatment and have applications in clinical trial and public safety settings. Self-reporting of alcohol use has clinical utility but lacks the desired reliability. Previously, proposed single-analyte biochemical tests of alcohol intake suffer from low sensitivity and specificity or examine only acute drinking and have therefore seen limited clinical use.

METHODS

To address this unmet need, plasma protein biomarker discovery and validation were performed with an alcohol self-administering nonhuman primate model system to develop a diagnostic that accurately classifies subjects into nondrinking, nonabusive drinking, and abusive drinking categories.

RESULTS

A 17-plasma protein panel was determined that correctly classifies abusive drinking with 100% sensitivity and also differentiates any level of drinking from alcohol abstinence with 88% accuracy.

CONCLUSIONS

The biomarker panel reflects changes in multiple organ systems and suggests robust changes in the plasma proteome with drinking that might serve as a sensitive and specific diagnostic test. The specific plasma proteins altered with alcohol self-administration might represent indicators of alcohol-induced stress on a variety of organ systems.

Nicotine: alcohol reward interactions

It is well established that the continued intake of drugs of abuse is reinforcing-that is repeated consumption increases preference. This has been shown in some studies to extend to other drugs of abuse; use of one increases preference for another. In particular, the present review deals with the interaction of nicotine and alcohol as it has been shown that smoking is a risk factor for alcoholism and alcohol use is a risk factor to become a smoker. The review discusses changes in the brain caused by chronic nicotine and chronic alcohol intake to approach the possible mechanisms by which one drug increases the preference for another. Chronic nicotine administration was shown to affect nicotine receptors in the brain, affecting not only receptor levels and distribution, but also receptor subunit composition, thus affecting affinity to nicotine. Other receptor systems are also affected among others catecholamine, glutamate, GABA levels and opiate and cannabinoid receptors. In addition to receptor systems and transmitters, there are endocrine, metabolic and neuropeptide changes as well induced by nicotine. Similarly chronic alcohol intake results in changes in the brain, in multiple receptors, transmitters and peptides as discussed in this overview and also illustrated in the tables. The changes are sex and age-dependent-some changes in males are different from those in females and in general adolescents are more sensitive to drug effects than adults. Although nicotine and alcohol interact-not all the changes induced by the combined intake of both are additive-some are opposing. These opposing effects include those on locomotion, acetylcholine metabolism, nicotine binding, opiate peptides, glutamate transporters and endocannabinoid content among others. The two compounds lower the negative withdrawal symptoms of each other which may contribute to the increase in preference, but the mechanism by which preference increases-most likely consists of multiple components that are not clear at the present time. As the details of induced changes of nicotine and alcohol differ, it is likely that the mechanisms of increasing nicotine preference may not be identical to that of increasing alcohol preference. Stimulation of preference of yet other drugs may again be different -representing one aspect of drug specificity of reward mechanisms.

MRI-guided dissection of the nonhuman primate brain: a case study

Numerous biochemical as well as electrophysiological techniques require tissue that must be retrieved very quickly following death in order to preserve the physiological integrity of the neuronal environment. Therefore, the ability to accurately predict the precise locations of brain regions of interest (ROI) and to retrieve those areas as quickly as possible following the brain harvest is critical for subsequent analyses. One way to achieve this objective is the utilization of high-resolution MRI to guide the subsequent dissections. In the present study, individual MRI images of the brains of rhesus and cynomolgus macaques that had chronically self-administered ethanol were employed in order to determine which blocks of dissected tissue contained specific ROIs. MRI-guided brain dissection of discrete brain regions was completely accurate in 100% of the cases. In comparison, approximately 60-70% accuracy was achieved in dissections that relied on external landmarks alone without the aid of MRI. These results clearly demonstrate that the accuracy of targeting specific brain areas can be improved with high-resolution MR imaging.

Glutamate plasticity in the drunken amygdala: the making of an anxious synapse

Plasticity at glutamatergic synapses is believed to be the cellular correlate of learning and memory. Classic fear conditioning, for example, is dependent upon NMDA-type glutamate receptor activation in the lateral/basolateral amygdala followed by increased synaptic expression of AMPA-type glutamate receptors. This review provides an extensive comparison between the initiation and expression of glutamatergic plasticity during learning/memory and glutamatergic alterations associated with chronic ethanol exposure and withdrawal. The parallels between these neuro-adaptive processes suggest that long-term ethanol exposure might "chemically condition" amygdala-dependent fear/anxiety via the increased function of pre- and post-synaptic glutamate signaling.

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.

The optimization of TaqMan real-time RT-PCR assay for transcriptional profiling of GABA-A receptor subunit plasticity

The GABA-A receptor plays a critical role in inhibitory neurotransmission in the brain. Quantitation of GABA-A receptor subunits in various brain regions is essential to understand their role in plasticity and brain disorders. However, conventional RNA assays are tedious and less sensitive for use in studies of subunit plasticity. Here we describe optimization of a sensitive assay of GABA-A receptor subunit gene expression by TaqMan real-time PCR. For each subunit gene, a set of primers and TaqMan fluorogenic probe were designed to specifically amplify the target template. The TaqMan methodology was optimized for quantification of mouse GABA-A receptor subunits (alpha(1-6), beta(1-3), gamma(2), and delta) and GAPDH. The TaqMan reaction detected very low levels of gene expression ( approximately 100 template copies of cDNA). A standard curve for GAPDH and one of the target genes, constructed using the cDNA, revealed slopes around -3.4 (r(2)=0.990), reflecting similar optimum PCR efficiencies. The methodology was utilized for quantification of the GABA-A receptor alpha(4)-subunit, which is known to upregulate following withdrawal from chronic progesterone or neurosteroids. Our results show that the alpha(4)-subunit expression increased threefold in the hippocampus following neurosteroid withdrawal in mice. The TaqMan PCR assay allows sensitive, high-throughput transcriptional profiling of complete GABA-A receptor subunit family, and thus provides specific tool for studies of GABA-A receptor subunit plasticity in neurological and psychiatric animal models.

The effects of chronic ethanol administration on amygdala neuronal firing and ethanol withdrawal seizures

Physical dependence on ethanol results in an ethanol withdrawal (ETX) syndrome including susceptibility to audiogenic seizures (AGS) in rodents after abrupt cessation of ethanol. Chronic ethanol administration and ETX induce functional changes of neurons in several brain regions, including the amygdala. Amygdala neurons are requisite elements of the neuronal network subserving AGS propagation during ETX induced by a subacute "binge" ethanol administration protocol. However, the effects of chronic ethanol administration on amygdala neuronal firing and ETX seizure behaviors are unknown. In the present study ethanol (5g/kg) was administered intragastrically in Sprague-Dawley rats once daily for 28days [chronic intermittent ethanol (CIE) protocol]. One week later the rats began receiving ethanol intragastrically three times daily for 4days (binge protocol). Microwire electrodes were implanted prior to CIE or on the day after CIE ended to record extracellular action potentials in lateral amygdala (LAMG) neurons. The first dose of ethanol administered in the binge protocol following CIE treatment did not alter LAMG neuronal firing, which contrasts with firing suppression seen previously in the binge protocol alone. These data indicate that CIE induces neuroadaptive changes in the ETX network which reduce LAMG response to ethanol. LAMG neuronal responses to acoustic stimuli prior to AGS were significantly decreased during ETX as compared to those before ethanol treatment. LAMG neurons fired tonically throughout the tonic convulsions during AGS. CIE plus binge treatment resulted in a significantly greater mean seizure duration and a significantly elevated incidence of death than was seen previously with the binge protocol alone, indicating an elevated seizure severity following chronic ethanol administration.

The role of GABA(A) receptors in the development of alcoholism

Alcoholism is a common, heritable, chronic relapsing disorder. GABA(A) receptors undergo allosteric modulation by ethanol, anesthetics, benzodiazepines and neurosteroids and have been implicated in the acute as well as the chronic effects of ethanol including tolerance, dependence and withdrawal. Medications targeting GABA(A) receptors ameliorate the symptoms of acute withdrawal. Ethanol induces plasticity in GABA(A) receptors: tolerance is associated with generally decreased GABA(A) receptor activation and differentially altered subunit expression. The dopamine (DA) mesolimbic reward pathway originating in the ventral tegmental area (VTA), and interacting stress circuitry play an important role in the development of addiction. VTA GABAergic interneurons are the primary inhibitory regulators of DA neurons and a subset of VTA GABA(A) receptors may be implicated in the switch from heavy drinking to dependence. GABA(A) receptors modulate anxiety and response to stress; important elements of sustained drinking and relapse. The GABA(A) receptor subunit genes clustered on chromosome 4 are highly expressed in the reward pathway. Several recent studies have provided strong evidence that one of these genes, GABRA2, is implicated in alcoholism in humans. The influence of the interaction between ethanol and GABA(A) receptors in the reward pathway on the development of alcoholism together with genetic and epigenetic vulnerabilities will be explored in this review.

Effects of mGlu1-receptor blockade on ethanol self-administration in inbred alcohol-preferring rats

The Group I family of metabotropic glutamate receptors includes subtype 1 (mGlu1) and subtype 5 (mGlu5) receptors. This family of receptors has generated interest as potential targets for different areas of therapeutic development, including intervention for alcohol and drug abuse. Most of this interest is driven by findings showing involvement of mGlu5 receptors in the regulation of drug self-administration; however, studies examining the role of mGlu1 receptors in drug self-administration are limited. The purpose of this work was to examine the role of mGlu1-receptor antagonism in the maintenance of ethanol self-administration and the self-administration of an alternate nondrug reward, sucrose. Male alcohol-preferring inbred rats were trained to self-administer ethanol (15% vol/vol) versus water on a concurrent schedule of reinforcement, and the effect of the mGlu1-receptor antagonist JNJ16259685 (0.1-1.0mg/kg intraperitoneal [IP]) was evaluated on self-administration. The rats were then trained to self-administer sucrose (0.4% wt/vol) versus water, and the same dose range of JNJ16259685 was tested. Locomotor activity was tested in a separate assessment to evaluate potential nonspecific motor effects of the antagonist. Ethanol self-administration was dose dependently reduced by JNJ16259685. This reduction was likely due to a motor impairment as the lowest effective dose (0.1mg/kg) significantly reduced locomotor behavior. Sucrose self-administration was reduced by the highest JNJ16259685 dose (1.0mg/kg), and this reduction was also likely due to a motor impairment. Interestingly, ethanol self-administration was more sensitive to mGlu1-receptor antagonism than sucrose self-administration as lower JNJ16259685 doses reduced ethanol-reinforced responding and motor behavior. Together, these results suggest that mGlu1 receptors do not play a specific role in modulating ethanol self-administration or the self-administration of an alternate nondrug reward (i.e., sucrose).

Chronic ethanol and withdrawal differentially modulate pre- and postsynaptic function at glutamatergic synapses in rat basolateral amygdala

Withdrawal anxiety is a significant factor contributing to continued alcohol abuse in alcoholics. This anxiety is long-lasting, can manifest well after the overt physical symptoms of withdrawal, and is frequently associated with relapse in recovering alcoholics. The neurobiological mechanisms governing these withdrawal-associated increases in anxiety are currently unknown. The basolateral amygdala (BLA) is a major emotional center in the brain and regulates the expression of both learned fear and anxiety. Neurotransmitter system alterations within this brain region may therefore contribute to withdrawal-associated anxiety. Because evidence suggests that glutamate-gated neurotransmitter receptors are sensitive to acute ethanol exposure, we examined the effect of chronic intermittent ethanol (CIE) and withdrawal (WD) on glutamatergic synaptic transmission in the BLA. We found that slices prepared from CIE and WD animals had significantly increased contributions by synaptic NMDA receptors. In addition, CIE increased the amplitude of AMPA-receptor-mediated spontaneous excitatory postsynaptic currents (sEPSCs), whereas only WD altered the amplitude and kinetics of tetrodotoxin-resistant spontaneous events (mEPSCs). Similarly, the frequency of sEPSCs was increased in both CIE and WD neurons, although only WD increased the frequency of mEPSCs. These data suggest that CIE and WD differentially alter both pre- and postsynaptic properties of BLA glutamatergic synapses. Finally, we show that microinjection of the AMPA-receptor antagonist, DNQX, can attenuate withdrawal-related anxiety-like behavior. Together, our results suggest that increased glutamatergic function may contribute to anxiety expressed during withdrawal from chronic ethanol.

Modulation of neuropeptide Y and Y1 receptor expression in the amygdala by fluctuations in the brain content of neuroactive steroids during ethanol drinking discontinuation in Y1R/LacZ transgenic mice

Previous studies have shown that GABAergic neuroactive steroids increase Y1 receptor (Y1R) gene expression in the amygdala of Y1R/LacZ transgenic mice, harbouring the murine Y1R gene promoter linked to a LacZ reporter gene. As ethanol is known to increase GABAergic neuroactive steroids, we investigated the relationship between fluctuations in the brain content of neuroactive steroids induced by chronic voluntary ethanol consumption or ethanol discontinuation and both the level of neuropeptide Y (NPY) immunoreactivity and Y1R gene expression in the amygdala of Y1R/LacZ transgenic mice. Ethanol discontinuation (48 h) after voluntary consumption of consecutive solutions of 3%, 6%, 10% and 20% (v/v) ethanol over 4 weeks produced an anxiety-like behaviour as measured by elevated plus maze. Voluntary ethanol intake increased the cerebrocortical concentration of the progesterone metabolite 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG) that returned to control level 48 h after discontinuation of ethanol intake. Ethanol discontinuation significantly decreased NPY immunoreactivity and concomitantly increased Y1R/LacZ transgene expression in the amygdala, whereas chronic ethanol intake failed to affect these parameters. The 5alpha-reductase inhibitor finasteride prevented both the increase in the cerebrocortical concentration of 3alpha,5alpha-TH PROG apparent after 4 weeks of ethanol intake and the changes in NPY immunoreactivity and transgene expression induced by ethanol discontinuation. Data suggest that 3alpha,5alpha-TH PROG plays an important role in the changes in NPY-Y1R signalling in the amygdala during ethanol discontinuation.

Long-term ethanol self-administration by the nonhuman primate, Macaca fascicularis, decreases the benzodiazepine sensitivity of amygdala GABA(A) receptors

BACKGROUND

Rodent models of chronic alcohol exposure are typically constrained to relatively short periods of forced ethanol due to the lifespan of these animals. Nonhuman primate models, particularly those employing long-term self-administration, are conceptually more similar to human alcoholic individuals.

METHODS

We performed whole-cell patch clamp recordings on acutely dissociated amygdala neurons isolated from cynomolgus macaque coronal temporal lobe slices. Slices were prepared from control monkeys or monkeys allowed to self-administer oral ethanol for 18 months. Flunitrazepam and acute ethanol modulation of currents gated by exogenous gamma-aminobutyric acid (GABA) application was assessed in these isolated neurons. Complementary experiments were performed on amygdala total RNA using quantitative real-time reverse transcription/polymerase chain reaction to understand potential ethanol-dependent adaptations to subunit composition.

RESULTS

Gamma-aminobutyric acid-gated currents from ethanol-exposed macaque amygdala neurons exhibited reduced modulation by flunitrazepam compared with control neurons. However, this was specific for benzodiazepines as the modest inhibition of GABA-gated currents by acute ethanol was not affected by the chronic ethanol consumption. We also measured mRNA expression levels for the beta, gamma, and delta subunits in total amygdala RNA isolated from control and ethanol-drinking animals. beta1 and gamma2 expression was significantly reduced in samples from ethanol-exposed amygdala.

CONCLUSIONS

Our findings demonstrate that chronic ethanol self-administration reduces the benzodiazepine sensitivity of amygdala GABA(A) receptors. This reduced sensitivity may be the result of decreased expression of an amygdala gamma subunit. These findings suggest that, while rodent and nonhuman primate models of chronic ethanol exposure share many characteristics, the specific molecular adaptations associated with the amygdala GABAergic system may not be identical.

Role of the amygdala in ethanol withdrawal seizures

Ethanol withdrawal (ETX) after induction of ethanol dependence results in a syndrome that includes enhanced seizure susceptibility. During ETX in rodents, generalized audiogenic seizures (AGS) can be triggered by intense acoustic stimulation. Previous studies have implicated specific brainstem nuclei in the neuronal network that initiates and propagates AGS during ETX. Although ethanol and ETX are known to affect amygdala neurons, involvement of the amygdala in the network subserving AGS is unclear. Since ethanol and ETX affect N-methyl-d-aspartate (NMDA) receptors in the amygdala, the present study evaluated the effect of focally microinjecting a NMDA antagonist into the amygdala of rats treated with a binge protocol (intragastric administration of ethanol 3 times daily for 4 days). Separate experiments examined extracellular neuronal firing in the amygdala. Cannulae or microwire electrodes were chronically implanted into the amygdala, and changes in seizure behaviors and/or extracellular action potentials were evaluated. Bilateral focal microinjection of a NMDA antagonist, 2-amino-7-phosphonoheptanoate (AP7), into either central nucleus or lateral nucleus of the amygdala (LAMG) significantly reduced AGS. The doses of AP7 and time course of effect were similar in each site, suggesting that both amygdala nuclei participate in the AGS network. Acoustic responses of LAMG neurons were significantly decreased 1 h after the first ethanol dose and also during ETX, as compared to pre-binge controls. However, LAMG neurons consistently exhibited rapid tonic firing during the generalized tonic convulsions of AGS. These findings suggest a critical role of the amygdala in the ETX seizure network in generating tonic convulsions during AGS.

Ethanol-Induced Regulation of GABAA Subunit mRNAs in Prefrontal Fields of Cynomolgus Monkeys

BACKGROUND

Recent evidence indicates that functional impairment of the orbital and medial fields of the prefrontal cortex may underlie the deficits in executive control of behavior that characterize addictive disorders, including alcohol addiction. Moreover, previous studies have indicated that alcohol alters GABA neurotransmission and one substrate of these effects may be through the reconfiguration of the subunits constituting the GABA(A) receptor complex. Given that GABAergic transmission has an integral role in cortical processing, influencing local and interregional communication, understanding alcohol-induced alterations in GABA(A) receptors in prefrontal fields of the primate brain may provide insight into the functional impairment of these brain regions in the alcohol-addicted state and extend our understanding of the molecular consequences of long-term use in these critical brain regions.

METHODS AND RESULTS

To address this problem, the effects of chronic ethanol self-administration in male cynomolgus monkeys on GABA(A) receptor subunit mRNA expression was studied in 3 frontal cortical fields: orbitofrontal cortex (OFC; area 13), anterior cingulate cortex (ACC; area 24), and the dorsolateral prefrontal cortex (DLPFC; area 46). Quantitative polymerase chain reaction revealed significant alterations in GABA(A) subunit mRNA expression in the OFC and DLPFC but not in the ACC. Specifically, expression of the alpha2, alpha4, beta1, beta3, and gamma1 to gamma3 subunit mRNAs was significantly less in the OFC, whereas the expression of beta1, beta2, gamma1, and delta subunit mRNAs was less in the DLPFC of alcohol-treated monkeys.

CONCLUSION

These findings suggest that ethanol-induced alterations in GABA(A) function may be due to alterations in GABA(A) subunit mRNA levels and subunit-specific alterations are selective to particular cortical fields.

Distinct functional characteristics of the lateral/basolateral amygdala GABAergic system in C57BL/6J and DBA/2J mice

It is generally understood that genetic mechanisms contribute to pathological anxiety and that C57BL/6 (B6) and DBA/2J (D2) mice, inbred strains differing markedly in their anxiety-like behaviors, may represent a model system to study these contributions. Because lateral/basolateral amygdala (BLA) GABA(A) receptors help regulate anxiety-like behaviors, we have tested the hypothesis that differences in receptor function/expression may be related to strain-specific differences in experimentally measured anxiety. First, we demonstrated that anxiety-like behaviors in two separate assays were more substantial in D2 mice. Then, using whole-cell electrophysiology of isolated neurons, we found that D2 BLA neurons expressed significantly greater GABA-gated responses than B6 BLA neurons. This was specific for GABA(A) receptors, because N-methyl-d-aspartate-gated responses were similar between strains. At the molecular level, this increased GABA(A) function was associated with higher levels of alpha 2 subunit mRNA expression in D2 BLA. Finally, to understand the ramifications of these functional and molecular biological differences, we examined both electrically evoked GABAergic responses and spontaneous synaptic currents using whole-cell recordings with in vitro slice preparations. Presynaptic GABAergic function was more robust in D2 compared with B6 slices. Together, our findings suggest that genetic mechanisms differentially represented in these two inbred mouse strains lead to robust differences in pre- and postsynaptic aspects of amygdala GABAergic function.

Ethanol potentiates GABAergic synaptic transmission in a postsynaptic neuron/synaptic bouton preparation from basolateral amygdala

Interactions between ethanol and synaptic transmission mediated by gamma -amino-N-butyric acid (GABA) have been suggested to contribute to alcohol intoxication. Ethanol effects on postsynaptic GABAA receptors have been the major focus of this line of research. There is increasing evidence that ethanol potentiation of GABAergic transmission involves increased GABA release from presynaptic terminals. In the present study, a mechanically isolated neuron/bouton preparation from the basolateral amygdala was used to examine the effects of ethanol on spontaneous GABAergic synaptic currents elicited by GABA release from the presynaptic terminals. We found that ethanol application produced a rapid increase in the frequency of spontaneous GABAergic synaptic currents. An acute tolerance to ethanol was also observed, and this tolerance involved GABAB receptor activation. The ethanol-induced potentiation did not involve alterations in the function of postsynaptic GABAA receptors and was independent of presynaptic action potential firing. These findings indicate that ethanol potentiates GABA release, most likely via a direct action on presynaptic boutons.

Apo-AII is an elevated biomarker of chronic non-human primate ethanol self-administration

AIMS

Serum protein profiles were examined in naïve, ethanol self-administering and ethanol abstinent cynomolgus monkeys (Macaca fasicularis) to search for differences in protein expression which could possibly serve as biomarkers of heavy ethanol consumption.

METHODS

Surface-enhanced laser desorption ionization time-of-flight (SELDI-ToF) mass spectrometry was used for proteomic profiling of serum.

RESULTS

Two proteins were identified by SELDI-ToF to be increased in ethanol self-administering compared with abstinent animals. These proteins were identified to be apolipoprotein AI (Apo-AI) and apolipoprotein AII (Apo-AII) by peptide mass fingerprinting and comparison with spectra of purified human Apo-AI and AII proteins. Immunoblot analysis of Apo-AI and Apo-AII was performed on a separate group of animals (within-animal ethanol-naïve and self-administering) and confirmed a statistically significant increase in Apo-AII, while Apo-AI was unchanged.

CONCLUSIONS

An open proteomic screen of serum and confirmation in a separate set of animals found Apo-AII to be increased in the serum of ethanol self-administering monkeys. These results are consistent with previous clinical studies of human ethanol consumption and serum apolipoprotein expression. Moreover, these results validate the use of non-human primates as a model organism for proteomic analysis of ethanol self-administration biomarkers.

Genetic and Other Contributions to Alcohol Intake in Rhesus Macaques (Macaca mulatta)

BACKGROUND

The etiology of alcoholism and alcohol abuse, like many other complex diseases, is heterogeneous and multifactorial. Numerous studies demonstrate a genetic contribution to variation in the expression of alcohol-related disorders in humans. Over the past decade, nonhuman primates have emerged as a valuable model for some aspects of human alcohol abuse because of their phylogenetic proximity to humans. Long-term, longitudinal studies of rhesus macaques (Macaca mulatta) have provided much insight into environmental influences, especially early life experiences, on alcohol consumption and behavior patterns that characterize alcohol intake later in life. It is not known, however, whether there is a genetic component as well to the variation seen in alcohol consumption in rhesus macaques. A significant genetic component to variation in alcohol consumption in rhesus macaques would show for the first time that like humans, for nonhuman primates additive genetic influences are important. Moreover, their use as a model for alcohol-related disorders in humans would have even greater relevance and utility for designing experiments incorporating the expanding molecular genetics field, and allow researchers to investigate the interaction among the known environmental influences and various genotypes.

METHODS

In this study, we investigate factors contributing to variation in alcohol consumption of 156 rhesus macaques collected over 10 years when subjects were adolescent in age, belonging to a single extended pedigree, with each cohort receiving identical early rearing backgrounds and subsequent treatments. To measure alcohol consumption each animal was provided unfettered simultaneous access both to an aspartame-sweetened 8.4% (v/v) alcohol-water solution, the aspartame-sweetened vehicle, and to water for 1 hour each day during the early afternoon between 13:00 and 15:00 in their home cages for a period of 5 to 7 weeks. We use multiple regression to identify factors that significantly affect alcohol consumption among these animals and a maximum likelihood program (ASReml) that, controlling for the significant factors, estimates the genetic contribution to the variance in alcohol consumption.

RESULTS

Multiple regression analysis identified test cohort and rearing environment as contributing to 57 and 2%, respectively, of the total variance in alcohol consumption. Of the remaining 41% of the variance about half (19.8%) was attributable to additive genetic effects using a maximum likelihood program.

CONCLUSION

This study demonstrates that, as in humans, there are additive genetic factors that contribute to variation in alcohol consumption in rhesus macaques, with other nongenetic factors accounting for substantial portions of the variance in alcohol consumption, Our findings show the presence of an additive genetic component and suggest the potential utility of the nonhuman primate as a molecular genetics tool for understanding alcohol abuse and alcoholism.

Chronic ethanol ingestion modulates proanxiety factors expressed in rat central amygdala

Withdrawal anxiety following chronic ethanol exposure is often associated with relapse in recovering alcoholics. It is likely that brain regions regulating anxiety-like behaviors adapt during chronic ethanol exposure to ultimately regulate such behaviors. The central amygdala contains numerous neurotransmitter systems that have been implicated in the regulation of anxiety-like behavior, including corticotropin releasing factor (CRF) and NMDA-type glutamate receptors. Chronic ethanol exposure causes functional adaptations in both CRF and NMDA receptors that are likely to regulate anxiety-like behaviors expressed during withdrawal. However, the molecular mechanisms governing these adaptations remain unexplored. We therefore evaluated these neurotransmitter systems in Sprague-Dawley rats during chronic ingestion of an ethanol-containing liquid diet. Quantitative real-time reverse transcription-PCR demonstrated that preproCRF mRNA was significantly upregulated by chronic ethanol exposure, whereas mRNA expression of CRF binding protein did not change. There were also no significant changes observed in any of the NMDA subunit mRNAs, although there was a trend toward greater NR2A mRNA expression during chronic ethanol exposure. Using Western blotting analysis we measured NMDA receptor subunit protein expression. Chronic ethanol exposure did not affect protein levels of the NR1 and NR2B subunits. Like the mRNA measures, chronic ethanol exposure did influence NR2A protein levels but the effects were modest. Our results demonstrate that NMDA receptor subunit mRNA and protein expressions are not strongly influenced by exposure to chronic ethanol. This suggests that the functional NMDA receptor adaptations identified in previous studies [Roberto, M., Schweitzer, P., Madamba, S. G., Stouffer, D. G., Parsons, L. H., & Siggins, G. R. (2004). Acute and chronic ethanol exposure alter glutamatergic transmission in rat central amygdala: an in vitro and in vivo analysis. J Neurosci 24, 1594-1603] are likely to be mediated by post-translational events. In contrast, enhanced levels of CRF during/after chronic ethanol exposure are likely to be mediated by increased levels of prepro CRF mRNA. Together, our findings suggest that adaptations to chronic ethanol exposure by proanxiety factors expressed in the central nucleus appear to be mediated by distinct cellular and molecular mechanisms.

Neuroimaging of Rodent and Primate Models of Alcoholism: Initial Reports From the Integrative Neuroscience Initiative on Alcoholism

Neuroimaging of animal models of alcoholism offers a unique path for translational research to the human condition. Animal models permit manipulation of variables that are uncontrollable in clinical, human investigation. This symposium, which took place at the annual meeting of the Research Society on Alcoholism in Vancouver, British Columbia, Canada, on June 29th, 2004, presented initial findings based on neuroimaging studies from the two centers of the Integrative Neuroscience Initiative on Alcoholism funded by the National Institute on Alcohol Abuse and Alcoholism. Effects of alcohol exposure were assessed with in vitro glucose metabolic imaging of rat brain, in vitro receptor imaging of monkey brain, in vivo magnetic resonance imaging of monkey brain, and in vivo magnetic resonance spectroscopic quantification of alcohol metabolism kinetics in rat brain.