Involvement of the Cyclic AMP-Responsive Element Binding Protein Gene Transcription Factor in Genetic Preference for Alcohol Drinking Behavior

Molecular mechanisms of alcohol's effects on the human body: A review and update

Alcohol consumption has been linked to numerous negative health outcomes although it has some beneficial effects on moderate dosages, the most severe of which being alcohol-induced hepatitis. The number of people dying from this liver illness has been shown to climb steadily over time, and its prevalence has been increasing. Researchers have found that alcohol consumption primarily affects the brain, leading to a wide range of neurological and psychological diseases. High-alcohol-consumption addicts not only experienced seizures, but also ataxia, aggression, social anxiety, and variceal hemorrhage that ultimately resulted in death, ascites, and schizophrenia. Drugs treating this liver condition are limited and can cause serious side effects like depression. Serine-threonine kinases, cAMP protein kinases, protein kinase C, ERK, RACK 1, Homer 2, and more have all been observed to have their signaling pathways disrupted by alcohol, and alcohol has also been linked to epigenetic changes. In addition, alcohol consumption induces dysbiosis by changing the composition of the microbiome found in the gastrointestinal tract. Although more studies are needed, those that have been done suggest that probiotics aid in keeping the various microbiota concentrations stable. It has been argued that reducing one's alcohol intake may seem less harmful because excessive drinking is a lifestyle disorder.

Targeting the Glucocorticoid Receptors During Alcohol Withdrawal to Reduce Protracted Neurocognitive Disorders

Persistent regional glucocorticoid (GC) dysregulation in alcohol-withdrawn subjects emerges as a key factor responsible for protracted molecular and neural alterations associated with long-term cognitive dysfunction. Regional brain concentrations of corticosterone vary independently from plasma concentrations in alcohol-withdrawn subjects, which may account for the treatment of alcohol withdrawal-induced persistent pathology. Thus, from a pharmacological point of view, a main issue remains to determine the relative efficacy of compounds targeting the GC receptors to attenuate or suppress the long-lasting persistence of brain regional GC dysfunctions in abstinent alcoholics, as well as persistent changes of neural plasticity. Data from animal research show that acting directly on GC receptors during the withdrawal period, via selective antagonists, can significantly counteract the development and persistence of cognitive and neural plasticity disorders during protracted abstinence. A critical remaining issue is to better assess the relative long-term efficacy of GC antagonists and other compounds targeting the corticotropic axis activity such as gamma-aminobutyric acid A (GABA_A) and GABA_B agonists. Indeed, benzodiazepines (acting indirectly on GABA_A receptors) and baclofen (agonist of the GABA_B receptor) are the compounds most widely used to reduce alcohol dependence. Clinical and preclinical data suggest that baclofen exerts an effective and more powerful counteracting action on such persistent cognitive and endocrine dysfunctions as compared to diazepam, even though its potential negative effects on memory processes, particularly at high doses, should be better taken into account.

Adolescent alcohol exposure epigenetically regulates CREB signaling in the adult amygdala

Binge alcohol drinking in adolescence leads to increased risk for alcohol use and other psychiatric disorders in adulthood. The transcription factor cAMP-response element binding (CREB) protein is involved in the neuronal response to adult ethanol exposure, but its role in the enduring effects of adolescent alcohol exposure in adulthood is unknown. We exposed male rats to adolescent intermittent ethanol (AIE) or saline (AIS) during post-natal days 28-41 and evaluated the epigenetic regulation of CREB dynamics in the adult amygdala. A subset of these adult rats was exposed to an acute ethanol challenge. AIE decreased CREB, phosphorylated CREB, CREB-binding protein (CBP) and p300 protein levels in adult amygdaloid brain structures. AIE exposure also causes deficits in Creb1, Cbp, and p300 mRNA expression in the amygdala of AIE adult rats which are normalized after acute ethanol exposure. Interestingly, occupancy of acetylated histone H3K9/14 proteins at specific locations in the Creb1, Cbp, and p300 gene promoter regions was decreased in the amygdala of AIE adult rats and was normalized by acute ethanol exposure. These results suggest that AIE exposure epigenetically reduces CREB and other related transcriptional activators in the amygdala in adulthood that may be associated with the behavioral effects of adolescent alcohol exposure.

Preclinical evaluation of avermectins as novel therapeutic agents for alcohol use disorders

The deleterious effects of alcohol use disorders (AUDs) on human health have been documented worldwide. The enormous socioeconomic burden coupled with lack of efficacious pharmacotherapies underlies the need for improved treatment strategies. At present, there is a growing body of preclinical evidence that demonstrates the potential of avermectins [ivermectin (IVM), selamectin (SEL), abamectin (ABM), and moxidectin (MOX)] in treatment of AUDs. Avermectins are derived by fermentation of soil micro-organism, Streptomyces avermitilis, and have been extensively used for treatment of parasitic infections. From the mechanistic standpoint, avermectins are positive modulators of purinergic P2X4 receptors (P2X4Rs). P2X4Rs belong to P2X superfamily of cation-permeable ion channels gated by adenosine 5'-triphosphate (ATP). Building evidence has implicated a role for P2X4Rs in regulation of ethanol intake and that ethanol can inhibit ATP-gated currents in P2X4Rs. Investigations using recombinant cell models and animal models of alcohol drinking have reported that IVM, ABM, and MOX, but not SEL, were able to antagonize the inhibitory effects of ethanol on P2X4Rs in vitro and reduce ethanol intake in vivo. Furthermore, IVM was shown to reduce ethanol consumption via P2X4R potentiation in vivo, supporting the involvement of P2X4Rs in IVM's anti-alcohol effects and that P2X4Rs can be used as a platform for developing novel anti-alcohol compounds. Taken together, these findings support the utility of avermectins as a novel class of drug candidates for treatment of AUDs.

Cyclic nucleotide phosphodiesterases: potential therapeutic targets for alcohol use disorder

Alcohol use disorder (AUD), which combines the criteria of both alcohol abuse and dependence, contributes as an important causal factor to multiple health and social problems. Given the limitation of current treatments, novel medications for AUD are needed to better control alcohol consumption and maintain abstinence. It has been well established that the intracellular signal transduction mediated by the second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) crucially underlies the genetic predisposition, rewarding properties, relapsing features, and systemic toxicity of compulsive alcohol consumption. On this basis, the upstream modulators phosphodiesterases (PDEs), which critically control intracellular levels of cyclic nucleotides by catalyzing their degradation, are proposed to play a role in modulating alcohol abuse and dependent process. Here, we highlight existing evidence that correlates cAMP and cGMP signal cascades with the regulation of alcohol-drinking behavior and discuss the possibility that PDEs may become a novel class of therapeutic targets for AUD.

Targeting Phosphodiesterases in Pharmacotherapy for Substance Dependence

Substance dependence is a chronic relapsing brain disorder associated with adaptational changes in synaptic plasticity and neuronal functions. The high levels of substance consumption and relapse rate suggest more reliable medications are in need to better address the underlying causes of this disease. It has been well established that the intracellular second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) and their signaling systems play an important role in the molecular mechanisms of substance taking behaviors. On this basis, the phosphodiesterase (PDE) superfamily, which crucially controls cyclic nucleotide levels by catalyzing their hydrolysis, has been proposed as a novel class of therapeutic targets for substance use disorders. This chapter reviews the expression patterns of PDEs in the brain with regard to neural structures underlying the dependent process and highlights available evidence for a modulatory role of PDEs in substance dependence.

Transcriptional Regulators as Targets for Alcohol Pharmacotherapies

Alcohol use disorder (AUD) is a chronic relapsing brain disease that currently afflicts over 15 million adults in the United States. Despite its prevalence, there are only three FDA-approved medications for AUD treatment, all of which show limited efficacy. Because of their ability to alter expression of a large number of genes, often with great cell-type and brain-region specificity, transcription factors and epigenetic modifiers serve as promising new targets for the development of AUD treatments aimed at the neural circuitry that underlies chronic alcohol abuse. In this chapter, we will discuss transcriptional regulators that can be targeted pharmacologically and have shown some efficacy in attenuating alcohol consumption when targeted. Specifically, the transcription factors cyclic AMP-responsive element binding protein (CREB), peroxisome proliferator-activated receptors (PPARs), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and glucocorticoid receptor (GR), as well as the epigenetic enzymes, the DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), will be discussed.

Adolescent Alcohol Exposure: Burden of Epigenetic Reprogramming, Synaptic Remodeling, and Adult Psychopathology

Adolescence represents a crucial phase of synaptic maturation characterized by molecular changes in the developing brain that shape normal behavioral patterns. Epigenetic mechanisms play an important role in these neuromaturation processes. Perturbations of normal epigenetic programming during adolescence by ethanol can disrupt these molecular events, leading to synaptic remodeling and abnormal adult behaviors. Repeated exposure to binge levels of alcohol increases the risk for alcohol use disorder (AUD) and comorbid psychopathology including anxiety in adulthood. Recent studies in the field clearly suggest that adolescent alcohol exposure causes widespread and persistent changes in epigenetic, neurotrophic, and neuroimmune pathways in the brain. These changes are manifested by altered synaptic remodeling and neurogenesis in key brain regions leading to adult psychopathology such as anxiety and alcoholism. This review details the molecular mechanisms underlying adolescent alcohol exposure-induced changes in synaptic plasticity and the development of alcohol addiction-related phenotypes in adulthood.

Reduction of alcohol drinking of alcohol-preferring (P) and high-alcohol drinking (HAD1) rats by targeting phosphodiesterase-4 (PDE4)

RATIONALE

Phosphodiesterase-4 (PDE4) and neuroimmune signaling have been posited to regulate alcohol drinking.

OBJECTIVES

This study evaluated the involvement of PDE4 and Il22ra2 on ethanol (EtOH) intake by alcohol-preferring (P) and high-alcohol-drinking (HAD1) rats.

METHODS

Exp 1 determined the dose-response effects of PDE4 inhibitors, rolipram, and Ro 20-1724, on 2 h/day free-choice EtOH intake by adult P and HAD1 rats. Exps 2-3 examined the effects of repeated administration with the PDE4 inhibitors on EtOH or sucrose intake and locomotor behavior. Exp 4 determined Pde4-associated gene expression differences in subregions of the extended amygdala, between high- and low-alcohol-consuming rat lines. Exp 5 evaluated the effects of infusing short hairpin RNA to knock down Il22ra2 in the nucleus accumbens (NAc) shell on a 24-h free-choice EtOH drinking by P rats.

RESULTS

Administration of rolipram or Ro 20-1724 reduced EtOH intake by P rats; Ro 20-1724 reduced EtOH intake by HAD1 rats. Repeated rolipram or Ro 20-1724 exposure reduced EtOH intake by P and HAD1 rats. PDE4 inhibition induced motor impairment during the first hour of EtOH intake by P rats. Higher gene expression levels for PDE4A were found in the NAc shell of P vs NP rats. ShRNAs targeting Il22ra2 in the NAc shell significantly reduced chronic EtOH intake.

CONCLUSIONS

PDE4 and neuroinflammatory/immune signaling pathways could represent molecular targets for the treatment of alcohol use disorders in genetically predisposed subjects. This study underscores the importance of testing compounds over multiple days and rat lines when determining efficacy to disrupt excessive alcohol intake.

Susceptibility to ethanol sensitization is differentially associated with changes in pCREB, trkB and BDNF mRNA expression in the mouse brain

Repeated exposure to ethanol in mice induces behavioural sensitization, a progressive increase in locomotor activity that is common to drugs of abuse. Not all mice however show sensitization to ethanol. The goal of the present study was to examine whether variability in the sensitization response to ethanol (EtOH) is differentially associated with regional brain changes in specific molecular markers associated with neuroplasticity, namely BDNF and its receptor trkB, and levels of phosphorylated cyclic AMP-regulated element-binding protein (pCREB), 14 days after withdrawal from chronic, intermittent EtOH exposure. Male DBA/2NCrl mice received 7 biweekly EtOH (2.2g/kg, i.p.) or saline (SAL) injections and were classified as Sensitized or Non-sensitized on the basis of final locomotor activity (LMA) scores. Brains were removed two weeks later for immunohistochemical and in situ hybridization analyses. Compared to SAL-treated and Non-sensitized mice, Sensitized animals showed a higher number of pCREB-immunoreactive cells in the nucleus accumbens shell (+68% and +50%, respectively) and in the bed nucleus of the stria terminalis (+61% and 46%, respectively), whereas SAL and Non-sensitized groups did not differ from each other. A different pattern was seen when BDNF and trkB mRNA levels were analyzed in the same groups. Non-sensitized mice displayed lower BDNF mRNA in several brain areas and significantly lower trkB levels throughout the brain when compared to either the Sensitized or to SAL groups, which did not differ from each other. These results indicate that sensitization to EtOH is differentially associated with increased pCREB levels in specific brain areas. The observed decrease in BDNF and trkB mRNA in the Non-sensitized group suggests the possibility that EtOH may have neurotoxic effects in a subpopulation of mice, which might in turn prevent the development of behavioural sensitization. The lack of a difference in BDNF and trkB mRNA expression between Sensitized and SAL mice suggests that EtOH sensitization may be mediated by mechanisms different from those mediating sensitization to other psychostimulants.

The phosphodiesterase-4 (PDE4) inhibitor rolipram decreases ethanol seeking and consumption in alcohol-preferring Fawn-Hooded rats

BACKGROUND

Alcohol dependence is a complex psychiatric disorder demanding development of novel pharmacotherapies. Because the cyclic adenosine monophosphate (cAMP) signaling cascade has been implicated in mediating behavioral responses to alcohol, key components in this cascade may serve as potential treatment targets. Phosphodiesterase-4 (PDE4), an enzyme that specifically catalyzes the hydrolysis of cAMP, represents a key point in regulating intracellular cAMP levels. Thus, it was of interest to determine whether PDE4 was involved in the regulation of alcohol use and abuse.

METHODS

Male Fawn-Hooded (FH/Wjd) rats were tested for 5% (v/v) ethanol (EtOH) and 10% (w/v) sucrose operant oral self-administration following treatment with the selective PDE4 inhibitor rolipram (0.0125, 0.025, or 0.05 mg/kg, subcutaneous [s.c.]); rolipram at higher doses (0.05, 0.1, and 0.2 mg/kg, s.c.) was tested to determine its impact on the intake of EtOH, sucrose, or water using the 2-bottle choice drinking paradigm. Subsequent open-field testing was performed to evaluate the influence of higher doses of rolipram on locomotor activity.

RESULTS

Acute administration of rolipram dose-dependently reduced operant self-administration of 5% EtOH, but had no effect on 10% sucrose responding. Time-course assessment revealed significant decreases in EtOH consumption after rolipram (0.1, 0.2 mg/kg) treatment in continuous- and intermittent access to EtOH at 5% or 10%, respectively. Moreover, chronic rolipram treatment time-dependently decreased 5% EtOH consumption and preference during treatment days and after the termination of rolipram administration. Rolipram at the highest doses (0.1 and 0.2 mg/kg) did decrease locomotor activity, but the effect lasted only 10 and 20 minutes, respectively, which did not likely alter long-term EtOH drinking.

CONCLUSIONS

These results suggest that PDE4 plays a role in alcohol seeking and consumption behavior. Drugs interfering with PDE4 may be a potential pharmacotherapy for alcohol dependence.

Fine mapping and expression of candidate genes within the chromosome 10 QTL region of the high and low alcohol-drinking rats

The high and low alcohol-drinking (HAD and LAD) rats were selectively bred for differences in alcohol intake. The HAD/LAD rats originated from the N/Nih heterogeneous stock developed from intercrossing eight inbred rat strains. The HAD×LAD F2 were genotyped, and a powerful analytical approach, using ancestral recombination and F2 recombination, was used to narrow a quantitative trait loci (QTL) for alcohol drinking to a 2-cM region on distal chromosome 10 that was in common in the HAD1/LAD1 and HAD2/LAD2 analyses. Quantitative real-time PCR was used to examine mRNA expression of six candidate genes (Crebbp, Trap1, Gnptg, Clcn7, Fahd1, and Mapk8ip3) located within the narrowed QTL region in the HAD1/LAD1 rats. Expression was examined in five brain regions, including the nucleus accumbens, amygdala, caudate putamen, hippocampus, and prefrontal cortex. All six genes showed differential expression in at least one brain region. Of the genes tested in this study, Crebbp and Mapk8ip3 may be the most promising candidates with regard to alcohol drinking.

Neuroscience of alcoholism: molecular and cellular mechanisms

Alcohol use and abuse appear to be related to neuroadaptive changes at functional, neurochemical, and structural levels. Acute and chronic ethanol exposure have been shown to modulate function of the activity-dependent gene transcription factor, cAMP-responsive element binding (CREB) protein in the brain, which may be associated with the development of alcoholism. Study of the downstream effectors of CREB have identified several important CREB-related genes, such as neuropeptide Y, brain-derived neurotrophic factor, activity-regulated cytoskeleton-associated protein, and corticotrophin-releasing factor, that may play a crucial role in the behavioral effects of ethanol and molecular changes in the specific neurocircuitry that underlie both alcohol addiction and a genetic predisposition to alcoholism. Brain chromatin remodeling due to histone covalent modifications may also be involved in mediating the behavioral effects and neuroadaptive changes that occur during ethanol exposure. This review outlines progressive neuroscience research into molecular and epigenetic mechanisms of alcoholism.

Stress, alcohol and drug interaction: an update of human research

A challenging question that continues unanswered in the field of addiction is why some individuals are more vulnerable to substance use disorders than others. Numerous risk factors for alcohol and other drugs of abuse, including exposure to various forms of stress, have been identified in clinical studies. However, the neurobiological mechanisms that underlie this relationship remain unclear. Critical neurotransmitters, hormones and neurobiological sites have been recognized, which may provide the substrates that convey individual differences in vulnerability to addiction. With the advent of more sophisticated measures of brain function in humans, such as functional imaging technology, the mechanisms and neural pathways involved in the interactions between drugs of abuse, the mesocorticolimbic dopamine system and stress systems are beginning to be characterized. This review provides a neuroadaptive perspective regarding the role of the hormonal and brain stress systems in drug addiction with a focus on the changes that occur during the transition from occasional drug use to drug dependence. We also review factors that contribute to different levels of hormonal/brain stress activation, which has implications for understanding individual vulnerability to drug dependence. Ultimately, these efforts may improve our chances of designing treatment strategies that target addiction at the core of the disorder.

The decreased cyclic-AMP dependent-protein kinase A function in the nucleus accumbens: a role in alcohol drinking but not in anxiety-like behaviors in rats

The nucleus accumbens (NAc) brain structures have been implicated in the reward and reinforcing properties of ethanol. The present study investigated the role of nucleus accumbal cyclic AMP (cAMP)-dependent protein kinase A (PKA) signaling in alcohol drinking and anxiety-like behaviors of rats. It was found that infusion of PKA inhibitor (Rp-cAMP) into the NAc shell significantly increased the alcohol but not the sucrose intake, without modulating the anxiety-like behaviors, as measured by elevated plus maze test in rats. PKA inhibitor infusion into the NAc shell significantly decreased the protein levels of alpha-catalytic subunit of PKA (PKA-Calpha) and phosphorylated cAMP response element-binding protein (p-CREB) as well as decreased the protein levels of neuropeptide Y (NPY) in the shell but not in the NAc core of rats. On the other hand, infusion of PKA activator (Sp-cAMP) or NPY alone into the NAc shell did not produce any changes in alcohol intake; however, when these agents were coinfused with PKA inhibitor, they significantly attenuated the increases in alcohol preference induced by pharmacological inhibition of PKA. Interestingly, PKA activator coinfusion with PKA inhibitor into the NAc shell significantly normalized the PKA inhibitor-induced decreases in the protein levels of PKA-Calpha and p-CREB as well as of NPY in the NAc shell of rats. Taken together, these results provide the first evidence that decreased PKA function in the NAc shell is involved in alcohol drinking but not in anxiety-like behaviors of rats. Furthermore, decreased function of PKA may regulate alcohol drinking behaviors via CREB-mediated decreased expression of NPY in the NAc shell of rats.

Ethanol-responsive genes: identification of transcription factors and their role in metabolomics

Transcription factors (TFs) and their combinatorial control on cis-regulatory elements play critical role in the co-expression of genes. This affects the interaction of genes in the transcriptome and thus may affect signals that cascade through cellular pathways. Using a combination of bioinformatic approaches, we sought to identify such common combinations of TFs in a set of ethanol-responsive (ER) genes and assess the role of ethanol in affecting multiple pathways through their co-regulation. Our results show that the metallothionein genes are regulated by TF motifs cAMP responsive element binding protein (CREB) and metal-activated transcription factor 1 and primarily involved in zinc ion homeostasis. We have also identified new target genes, Synaptojanin 1 and tryptophan hydroxylase 1, potentially regulated by this module. Altered arrangement of TF-binding sites in the module may direct the action of these and other target genes in intracellular signaling cascades, cell growth and/or maintenance. In addition to CREB, other key TFs identified are ecotropic viral integration site-1 and SP1. These modulate the contribution of the target ER genes in cell cycle regulation and apoptosis or programmed cell death. Multiple lines of evidence confirm the above findings and indicate that different groups of ER genes are involved in different biological processes and their co-regulation most likely results from different sets of regulatory modules. These findings associate the role of the ER genes studied and their potential TF modules with alcohol response pathways and phenotypes.

Deficits in amygdaloid cAMP-responsive element-binding protein signaling play a role in genetic predisposition to anxiety and alcoholism

We investigated the role of cAMP-responsive element-binding protein (CREB) in genetic predisposition to anxiety and alcohol-drinking behaviors using alcohol-preferring (P) and -nonpreferring (NP) rats. The levels of CREB, phosphorylated CREB, and neuropeptide Y (NPY) were innately lower in the central amygdala (CeA) and medial amygdala (MeA), but not in the basolateral amygdala (BLA), of P rats compared with NP rats. P rats displayed higher baseline anxiety-like behaviors and consumed higher amounts of alcohol compared with NP rats. Ethanol injection or voluntary intake reduced the higher anxiety levels in P rats. Ethanol also increased CREB function in the CeA and MeA, but not in the BLA, of P rats. Infusion of the PKA activator Sp-cAMP or NPY into the CeA decreased the alcohol intake and anxiety-like behaviors of P rats. PKA activator infusion also increased CREB function in the CeA of P rats. On the other hand, ethanol injection or voluntary intake did not produce any changes either in anxiety levels or on CREB function in the amygdaloid structures of NP rats. Interestingly, infusion of the PKA inhibitor Rp-cAMP into the CeA provoked anxiety-like behaviors and increased alcohol intake in NP rats. PKA inhibitor decreased CREB function in the CeA of NP rats. These novel results provide the first evidence to our knowledge that decreased CREB function in the CeA may be operative in maintaining the high anxiety and excessive alcohol-drinking behaviors of P rats.

The "ups and downs" of signaling cascades in addiction

Drug addiction is a chronic disease characterized by compulsive drug use despite the severe negative consequences associated with it. Repeated exposure to drugs of abuse results in molecular adaptations in neuronal signaling pathways, which eventually manifest in the complex behavioral alterations that characterize addiction. These include tolerance, sensitization, dependence, drug craving, and relapse. In this Review, we focus on recent studies highlighting signaling cascades initiated by cocaine, as a representative of a drug of abuse with a defined site of action, and alcohol, as a drug with an undefined primary site of action. Specifically, we describe recent studies that emphasize the role of protein-protein interactions, phosphorylation, and compartmentalization in the molecular mechanisms that result in the cellular and behavioral adaptations that underlie addiction. Signaling cascades that contribute to addiction, as well as those that protect or delay the development of addiction, are presented.

CREB Gene Transcription Factors: Role in Molecular Mechanisms of Alcohol and Drug Addiction

This article presents the proceedings of a symposium presented at the meeting of the Research Society on Alcoholism, held in Vancouver, British Columbia, Canada, in June 2004. The organizers and chairpersons were Subhash C. Pandey and Fulton Crews. The presentations were (1) Ethanol Modulation of CREB: Role in Dependence and Withdrawal, by Fulton Crews; (2) Effects of D1 Dopamine Receptor Activation During Withdrawal From Chronic Morphine: Enhanced CREB Activation and Decreased Conditioned Place Aversion, by Elena H. Chartoff; (3) CREB-Haplodeficient Mice: Role in Anxiety and Alcohol-Drinking Behaviors, by Subhash C. Pandey; and (4) A Role for CREB in Stress and Drug Addiction, by Julie A. Blendy.

Alcohol and gene expression in the central nervous system

AIMS

To describe recent research focusing on the analysis of gene and protein expression relevant to understanding ethanol consumption, dependence and effects, in order to identify common themes.

METHODS

A selective literature search was used to collate the relevant data.

RESULTS

Over 160 genes have been individually assessed before or after ethanol administration, as well as in genetically selected lines. Techniques for studying gene expression include northern blots, differential display, real time reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. More recently, high throughput functional genomic technology, such as DNA microarrays, has been used to examine gene expression. Recent gene expression analyses have dramatically increased the number of candidate genes (nine array papers have illuminated 600 novel gene transcripts that may contribute to alcohol abuse and alcoholism).

CONCLUSIONS

Although functional genomic experiments (transcriptome analysis) have failed to identify a single alcoholism gene, they have illuminated important pathways and gene products that may contribute to the risk of alcohol abuse and alcoholism.

The gene transcription factor cyclic AMP-responsive element binding protein: role in positive and negative affective states of alcohol addiction

The gene transcription factor cyclic adenosine monophosphate (cAMP)-responsive element binding (CREB) protein is a nuclear protein that regulates synaptic plasticity via modulating the expression of several (cAMP)-inducible genes. Alcohol addiction is a complex psychiatric disorder and is characterized by a compulsive and uncontrolled pattern of alcohol drinking by an individual in spite of the adverse consequences of its abuse. Ethanol produces both euphoric (reward and reinforcing) and dysphoric (negative withdrawal reactions) effects and these are most likely involved in the initiation and maintenance of alcohol use and abuse. Several neurotransmitter systems in the brain might be involved in the effects of alcohol but the exact molecular mechanisms of both the positive and negative affective states of alcohol abuse are still unclear. Recent research in molecular neurosciences using animal models have identified the role of extended amygdaloid (shell structures of nucleus accumbens [NAc] and central and medial amygdaloid nuclei) CREB signaling in positive and negative affective states of alcohol drinking behaviors. This review article highlights the current findings on the role of nucleus accumbal and amygdaloid CREB signaling in behavioral consequences of alcohol use and abuse.

Differences in basal levels of CREB and NPY in nucleus accumbens regions between C57BL/6 and DBA/2 mice differing in inborn alcohol drinking behavior

An increasing body of evidence suggests that genetic factors play a role in alcohol drinking behaviors. C57BL/6J (C57) mice innately consume larger amounts of alcohol compared to that consumed by DBA/2J (DBA) mice. Furthermore, alterations in cAMP-responsive element binding (CREB) protein function in the brain have been implicated in alcohol drinking behaviors. The present investigation examined innate expression and phosphorylation of CREB in various brain structures of C57 and DBA mice. It was found that CREB expression and phosphorylation was lower, specifically in the shell structure of the nucleus accumbens, in C57 mice compared to that in DBA mice. CREB expression and phosphorylation were similar in other brain regions such as the nucleus accumbens core and the cortical, amygdaloid, hippocampal, and striatal structures of C57 and DBA mice. The expression of a cAMP-inducible gene, neuropeptide Y (NPY), was also investigated in the nucleus accumbens region of C57 and DBA mice. It was found that in C57 mice, NPY protein levels were lower in the shell but not in the core structure of the nucleus accumbens compared to that in DBA mice. It was also found that C57 mice are not innately anxious, but they consume larger amounts of alcohol than do DBA mice. Because the shell structure of the nucleus accumbens has been implicated in reward mechanisms of alcohol, it is possible that lower CREB function in this brain structure may be in part associated with the excessive alcohol drinking behavior of C57 mice.

Anxiety and alcohol abuse disorders: a common role for CREB and its target, the neuropeptide Y gene

It has been hypothesized that anxiety disorders play an important role in the initiation and maintenance of alcohol drinking behaviors. However, the molecular mechanisms for the association between anxiety and alcohol abuse are not well understood. Structures of the extended amygdala, particularly the central nucleus of amygdala, are involved in anxiety and in motivational aspects of alcohol drinking behaviors. Here, I propose that cAMP response element-binding protein (CREB) has a role in anxiety and alcohol drinking behaviors. The CREB gene transcription factor regulates the expression of the gene encoding neuropeptide Y (NPY), and decreased concentrations of NPY are implicated in anxiety and alcohol drinking behaviors. Therefore, decreased function of CREB in the central nucleus of the amygdala might regulate anxiety and alcohol intake via decreased expression of NPY, and might provide a common link between anxiety and alcohol abuse disorders. I also suggest that, via CREB, NPY might interact with other CREB target genes, such as the gene encoding brain-derived neurotrophic factor, and that this CREB-mediated interaction might be important in the regulation of anxiety and alcohol drinking behaviors.

Congenitally learned helpless rats show abnormalities in intracellular signaling

BACKGROUND

Affective disorders and the drugs used to treat them lead to changes in intracellular signaling. We used a genetic animal model to investigate to what extent changes in intracellular signal transduction confer a vulnerability to mood or anxiety disorders.

METHODS

Levels of gene expression in a selectively bred strain of rats with a high vulnerability to develop congenitally learned helplessness (cLH), a strain highly resistant to the same behavior (cNLH) and outbred Sprague-Dawley (SD) control animals were compared using quantitative reverse transcription polymerase chain reaction.

RESULTS

Congenitally learned helpless animals had a 24%-30% reduced expression of the cyclic adenosine monophosphate response element binding protein messenger ribonucleic acid (mRNA) in the hippocampus and a 40%-41% increased level of the antiapoptotic protein bcl-2 mRNA in the prefrontal cortex compared to cNLH and SD rats. Other significant changes included changes in the expression levels of the alpha catalytic subunit of protein kinase A, glycogen synthase kinase 3beta, and protein kinase C epsilon.

CONCLUSIONS

Congenitally learned helpless animals show evidence of altered signal transduction and regulation of apoptosis compared to cNLH and SD control animals.

The decreased phosphorylation of cyclic adenosine monophosphate (cAMP) response element binding (CREB) protein in the central amygdala acts as a molecular substrate for anxiety related to ethanol withdrawal in rats

BACKGROUND

Several lines of evidence indicate a high comorbidity between anxiety and alcohol abuse. This study investigated the molecular mechanisms in the amygdaloid neurocircuitry governing anxiety related to ethanol withdrawal and also the phenomenon of alcohol preference.

METHODS

Male Sprague Dawley(R) rats were treated with ethanol or control diet for 15 days, and ethanol-fed rats were withdrawn for 0 and 24 hr. Ethanol-withdrawn or control diet-fed rats were bilaterally infused into central or basolateral amygdala with artificial cerebrospinal fluid or protein kinase A (PKA) activator or inhibitor. These rats were used to measure anxiety levels by the elevated plus-maze test. Protein levels of various signaling molecules related to cyclic adenosine monophosphate (cAMP)-response element binding (CREB) protein signaling in amygdaloid structures were determined by gold immunolabeling procedure. The messenger RNA levels of neuropeptide Y were determined by in situ polymerase chain reaction procedure.

RESULTS

Ethanol withdrawal (24 hr) after chronic exposure (15 days) produced anxiety in rats as measured by elevated plus-maze test. Ethanol withdrawal but not treatment significantly decreased the phosphorylation of CREB protein and protein levels of Ca2+/calmodulin-dependent protein kinase IV without modulating the protein levels of total CREB and alpha-catalytic subunit of protein kinase A (PKA-Calpha) in the central and medial amygdala. However, these changes were not observed in the basolateral amygdala. We also investigated the effects of manipulation of the phosphorylation status of CREB in the central amygdala by infusion of the PKA activator (Sp-cAMPS) or inhibitor (Rp-cAMPS) on anxiety levels in rats during ethanol withdrawal. When Sp-cAMPS is specifically infused into the central amygdala, it dose-dependently normalizes the decrease in CREB phosphorylation and prevents the development of anxiety in rats during ethanol withdrawal. On the other hand, Rp-cAMPS infusions into the central or basolateral amygdala decrease CREB phosphorylation, but only infusion into the central amygdala provokes anxiety and increases alcohol preference in normal rats. We also found that alcohol preference provoked by decreased CREB phosphorylation is related to decreased expression of the neuropeptide Y gene in the central amygdala.

CONCLUSIONS

These novel results suggest the possibility that decreased CREB phosphorylation in the central amygdala acts as a common molecular correlate for anxiety and alcohol-drinking behaviors and also is correlated with anxiety related to ethanol withdrawal.

Neuropeptide y and alcoholism: genetic, molecular, and pharmacological evidence

This article presents the proceedings of a symposium presented at the combined meeting of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism, held in San Francisco, CA, in June 2002. The organizers and chairpersons were Subhash C. Pandey and Todd E. Thiele. The presentations were (1) Altered ethanol-induced sedation and ethanol drinking in mutant mice lacking specific NPY receptor, by Todd E. Thiele; (2) NPY in P and NP rats: polymorphism and mRNA expression, by Lucinda G. Carr; (3) The cAMP-dependent PKA in the central amygdala regulates alcohol intake through NPY gene, by Subhash C. Pandey; (4) Involvement of NPY in alcohol dependence: from animal models to human genetics, by Markus Heilig; and (5) Association of neuropeptide Y polymorphism with the occurrence of type 1 and type 2 alcoholism, by Erkki Ilveskoski.

Estrogen affects the expression of Ca2+/calmodulin-dependent protein kinase IV in amygdala

We examined the effects of long-term estradiol benzoate (E2) treatment on protein expression of Ca2+/calmodulin-dependent protein kinase IV (CaMK IV) in the amygdala of ovariectomized (OVX) rats. Western blot analysis revealed increased protein levels of CaMK IV in the nuclear but not in the membranal or cystolic fraction of total amygdala in E2-treated compared to OVX rats. Significant increases in levels of CaM kinase IV gold immunolabeling were seen in the medial and basomedial, but not in the central or basolateral, amygdala of E2 compared to OVX rats, indicating the neuroanatomical heterogeneity of the E2 effect. These results suggest that CaMK IV may act as a molecular target for actions of estrogen in the amygdala of rats.

Effects of protracted nicotine exposure and withdrawal on the expression and phosphorylation of the CREB gene transcription factor in rat brain

Addiction to nicotine may result in molecular adaptations in the neurocircuitry of specific brain structures via changes in the cyclic AMP-responsive element binding protein (CREB)-dependent gene transcription program. We therefore investigated the effects of chronic nicotine exposure and its withdrawal on CREB and phosphorylated CREB (p-CREB) protein levels in the rat brain. We report here that chronic nicotine exposure (1-h withdrawal) had no effect on the expression of CREB and p-CREB in the rat cortex and amygdala. On the other hand, decreases in the expression of CREB protein and phosphorylation of CREB occur in the cingulate gyrus, and in the parietal and the piriform but not in the frontal cortex during nicotine withdrawal (18 h) after nicotine exposure. It was also observed that CREB and p-CREB protein levels were significantly decreased in the medial and basolateral, but not in the central amygdala during nicotine withdrawal (18 h) after chronic nicotine exposure. Furthermore, it was found that nicotine withdrawal (18 h) after chronic nicotine exposure leads to decreased CRE-DNA binding without modulating cAMP-dependent protein kinase A activity in the cortex and the amygdala of rats. In addition, chronic nicotine treatment produced anxiolytic effects whereas nicotine withdrawal (18 h) produced anxiety in rats as measured by the elevated plus-maze test. These results provide the first evidence that decreased CREB activity and/or expression in specific cortical and amygdaloid brain structures may be involved in the underlying molecular mechanisms of nicotine dependence.