Drug challenges reveal differences in mediation of stress facilitation of voluntary alcohol drinking and withdrawal-induced anxiety in alcohol-preferring P rats

Neurobiological Bases of Alcohol Consumption After Social Stress

The urge to seek and consume excessive alcohol is intensified by prior experiences with social stress, and this cascade can be modeled under systematically controlled laboratory conditions in rodents and non-human primates. Adaptive coping with intermittent episodes of social defeat stress often transitions to maladaptive responses to traumatic continuous stress, and alcohol consumption may become part of coping responses. At the circuit level, the neural pathways subserving stress coping intersect with those for alcohol consumption. Increasingly discrete regions and connections within the prefrontal cortex, the ventral and dorsal striatum, thalamic and hypothalamic nuclei, tegmental areas as well as brain stem structures begin to be identified as critical for reacting to and coping with social stress while seeking and consuming alcohol. Several candidate molecules that modulate signals within these neural connections have been targeted in order to reduce excessive drinking and relapse. In spite of some early clinical failures, neuropeptides such as CRF, opioids, or oxytocin continue to be examined for their role in attenuating stress-escalated drinking. Recent work has focused on neural sites of action for peptides and steroids, most likely in neuroinflammatory processes as a result of interactive effects of episodic social stress and excessive alcohol seeking and drinking.

Corticotropin-Releasing Factor (CRF) Neurocircuitry and Neuropharmacology in Alcohol Drinking

Alcohol use is pervasive in the United States. In the transition from nonhazardous drinking to hazardous drinking and alcohol use disorder, neuroadaptations occur within brain reward and brain stress systems. One brain signaling system that has received much attention in animal models of excessive alcohol drinking and alcohol dependence is corticotropin-releasing factor (CRF). The CRF system is composed of CRF, the urocortins, CRF-binding protein, and two receptors - CRF type 1 and CRF type 2. This review summarizes how acute, binge, and chronic alcohol dysregulates CRF signaling in hypothalamic and extra-hypothalamic brain regions and how this dysregulation may contribute to changes in alcohol reinforcement, excessive alcohol consumption, symptoms of negative affect during withdrawal, and alcohol relapse. In addition, it summarizes clinical work examining CRF type 1 receptor antagonists in humans and discusses why the brain CRF system is still relevant in alcohol research.

Rat animal models for screening medications to treat alcohol use disorders

The purpose of this review is to present animal research models that can be used to screen and/or repurpose medications for the treatment of alcohol abuse and dependence. The focus will be on rats and in particular selectively bred rats. Brief introductions discuss various aspects of the clinical picture, which provide characteristics of individuals with alcohol use disorders (AUDs) to model in animals. Following this, multiple selectively bred rat lines will be described and evaluated in the context of animal models used to screen medications to treat AUDs. Next, common behavioral tests for drug efficacy will be discussed particularly as they relate to stages in the addiction cycle. Tables highlighting studies that have tested the effects of compounds using the respective techniques are included. Wherever possible the Tables are organized chronologically in ascending order to describe changes in the focus of research on AUDs over time. In general, high ethanol-consuming selectively bred rats have been used to test a wide range of compounds. Older studies usually followed neurobiological findings in the selected lines that supported an association with a propensity for high ethanol intake. Most of these tests evaluated the compound's effects on the maintenance of ethanol drinking. Very few compounds have been tested during ethanol-seeking and/or relapse and fewer still have assessed their effects during the acquisition of AUDs. Overall, while a substantial number of neurotransmitter and neuromodulatory system targets have been assessed; the roles of sex- and age-of-animal, as well as the acquisition of AUDs, ethanol-seeking and relapse continue to be factors and behaviors needing further study. This article is part of the Special Issue entitled "Alcoholism".

Emerging pharmacotherapies for alcohol use disorder

The identification of different stages within the alcohol use disorder (AUD) cycle that are linked to neurocircuitry changes in pathophysiology associated with the negative emotional states of abstinence has provided a view of medication development for AUD that emphasizes changes in the brain reward and stress systems. Alcohol use disorder can be defined as a chronic relapsing disorder that involves compulsive alcohol seeking and taking, loss of control over alcohol intake, and emergence of a negative emotional state during abstinence. The focus of early medications development was to block the motivation to seek alcohol in the binge/intoxication stage. More recent work has focused on reversing the motivational dysregulations associated with the withdrawal/negative affect and preoccupation/anticipation stages during protracted abstinence. Advances in our understanding of the neurocircuitry and neuropharmacological mechanisms that are involved in the development and maintenance of the withdrawal/negative affect stage using validated animal models have provided viable targets for future medications. Another major advance has been proof-of-concept testing of potential therapeutics and clinical validation of relevant pharmacological targets using human laboratory models of protracted abstinence. This review focuses on future targets for medication development associated with reversal of the loss of reward function and gain in brain stress function that drive negative reinforcement in the withdrawal/negative affect stage of addiction. Basic research has identified novel neurobiological targets associated with the withdrawal/negative affect stage and preoccupation/anticipation stage, with a focus on neuroadaptive changes within the extended amygdala that account for the transition to dependence and vulnerability to relapse. This article is part of the Special Issue entitled "Alcoholism".

An Update on CRF Mechanisms Underlying Alcohol Use Disorders and Dependence

Alcohol is the most commonly used and abused substance worldwide. The emergence of alcohol use disorders, and alcohol dependence in particular, is accompanied by functional changes in brain reward and stress systems, which contribute to escalated alcohol drinking and seeking. Corticotropin-releasing factor (CRF) systems have been critically implied in the transition toward problematic alcohol drinking and alcohol dependence. This review will discuss how dysregulation of CRF function contributes to the vulnerability for escalated alcohol drinking and other consequences of alcohol consumption, based on preclinical evidence. CRF signaling, mostly via CRF1 receptors, seems to be particularly important in conditions of excessive alcohol taking and seeking, including during early and protracted withdrawal, relapse, as well as during withdrawal-induced anxiety and escalated aggression promoted by alcohol. Modulation of CRF1 function seems to exert a less prominent role over low to moderate alcohol intake, or to species-typical behaviors. While CRF mechanisms in the hypothalamic-pituitary-adrenal axis have some contribution to the neurobiology of alcohol abuse and dependence, a pivotal role for extra-hypothalamic CRF pathways, particularly in the extended amygdala, is well characterized. More recent studies further suggest a direct modulation of brain reward function by CRF signaling in the ventral tegmental area, nucleus accumbens, and the prefrontal cortex, among other structures. This review will further discuss a putative role for other components of the CRF system that contribute for the overall balance of CRF function in reward and stress pathways, including CRF2 receptors, CRF-binding protein, and urocortins, a family of CRF-related peptides.

Stress and Withdrawal from Chronic Ethanol Induce Selective Changes in Neuroimmune mRNAs in Differing Brain Sites

Stress is a strong risk factor in alcoholic relapse and may exert effects that mimic aspects of chronic alcohol exposure on neurobiological systems. With the neuroimmune system becoming a prominent focus in the study of the neurobiological consequences of stress, as well as chronic alcohol exposure proving to be a valuable focus in this regard, the present study sought to compare the effects of stress and chronic ethanol exposure on induction of components of the neuroimmune system. Rats were exposed to either 1 h exposure to a mild stressor (restraint) or exposure to withdrawal from 15 days of chronic alcohol exposure (i.e., withdrawal from chronic ethanol, WCE) and assessed for neuroimmune mRNAs in brain. Restraint stress alone elevated chemokine (C–C motif) ligand 2 (CCL2), interleukin-1-beta (IL-1β), tumor necrosis factor alpha (TNFα) and toll-like receptor 4 (TLR4) mRNAs in the cerebral cortex within 4 h with a return to a control level by 24 h. These increases were not accompanied by an increase in corresponding proteins. Withdrawal from WCE also elevated cytokines, but did so to varying degrees across different cytokines and brain regions. In the cortex, stress and WCE induced CCL2, TNFα, IL-1β, and TLR4 mRNAs. In the hypothalamus, only WCE induced cytokines (CCL2 and IL-1β) while in the hippocampus, WCE strongly induced CCL2 while stress and WCE induced IL-1β. In the amygdala, only WCE induced CCL2. Finally—based on the previously demonstrated role of corticotropin-releasing factor 1 (CRF1) receptor inhibition in blocking WCE-induced cytokine mRNAs—the CRF1 receptor antagonist CP154,526 was administered to a subgroup of stressed rats and found to be inactive against induction of CCL2, TNFα, or IL-1β mRNAs. These differential results suggest that stress and WCE manifest broad neuroimmune effects in brain depending on the cytokine and brain region, and that CRF inhibition may not be a relevant mechanism in non-alcohol exposed animals. Overall, these effects are complex in terms of their neuroimmune targets and neuroanatomical specificity. Further investigation of the differential distribution of cytokine induction across neuroanatomical regions, individual cell types (e.g., neuronal phenotypes and glia), severity of chronic alcohol exposure, as well as across differing stress types may prove useful in understanding differential mechanisms of induction and for targeting select systems for pharmacotherapeutic intervention in alcoholism.

Nucleus accumbens lentiviral-mediated gain of function of the oxytocin receptor regulates anxiety- and ethanol-related behaviors in adult mice

Anxiety is believed to influence ethanol use human in alcoholics. Studies using laboratory animals suggested an interaction between oxytocin and the behavioral effects of ethanol. Our previous study implicated a potential role for the oxytocin receptor (OxtR) in regulating ethanol-conditioned place preference. Here, we examined anxiety and the behavioral responses to ethanol in C57BL/6 mice stereotaxically injected in the nucleus accumbens (NAcc) with lentiviral vectors expressing an empty vector (Mock) or the OxtR cDNA. For anxiety we used the elevated-plus maze, the open-field and the marble-burying tests and for ethanol we used the two-bottle choice paradigm, the wire-hanging and ethanol-induced loss-of-righting-reflex tests. We found that, compared to Mock, OxtR overexpression led to anxiolytic-like behavior without altering spontaneous locomotor activity. Most importantly, we found that, relative to Mock controls, increased expression of the OxtR in the NAcc led to decreased ethanol consumption and preference in the two-bottle choice protocol and increased resistance to ethanol-induced sedation. We also compared the consequence of OxtR modulation on the consumption and preference of saccharin and quinine and found that the two experimental groups did not differ for any tastant. These results provide further evidence that the oxytocin system contributes to the regulation of ethanol drinking and sensitivity and position OxtR as a central molecular mediator of ethanol's effects within the mesolimbic system. Taken together, the current findings suggest that OxtR manipulation may be a relevant strategy to address ethanol use disorders.

β-Endorphin neuronal transplantation into the hypothalamus alters anxiety-like behaviors in prenatal alcohol-exposed rats and alcohol-non-preferring and alcohol-preferring rats

BACKGROUND

Alcohol exposure has adverse effects on stress physiology and behavioral reactivity. This is suggested to be due, in part, to the effect of alcohol on β-endorphin (β-EP)-producing neurons in the hypothalamus. In response to stress, β-EP normally provides negative feedback to the hypothalamic-pituitary-adrenal axis and interacts with other neurotransmitter systems in the amygdala to regulate behavior. We examined whether β-EP neuronal function in the hypothalamus reduces the corticosterone response to acute stress, attenuates anxiety-like behaviors, and modulates alcohol drinking in rats.

METHODS

To determine whether β-EP neuronal transplants modulate the stress response, anxiety behavior, and alcohol drinking, we implanted differentiated β-EP neurons into the paraventricular nucleus (PVN) of the hypothalamus of normal, prenatal alcohol-exposed, and alcohol-preferring (P) and alcohol-non-preferring (NP) rats. We then assessed corticosterone levels in response to acute restraint stress and other markers of stress response in the brain and anxiety-like behaviors in the elevated plus maze and open-field assays.

RESULTS

We showed that β-EP neuronal transplants into the PVN reduced the peripheral corticosterone response to acute stress and attenuated anxiety-like behaviors. Similar transplants completely reduced the hypercorticosterone response and elevated anxiety behaviors in prenatal alcohol-exposed adult rats. Moreover, we showed that β-EP reduced anxiety behavior in P rats with minimal effects on alcohol drinking during and following restraint stress.

CONCLUSIONS

These data further establish a role of β-EP neurons in the hypothalamus for regulating physiological stress response and anxiety behavior and resemble a potential novel therapy for treating stress-related psychiatric disorders in prenatal alcohol-exposed children and those genetically predisposed to increased alcohol consumption.

Existing and Future Drugs for the Treatment of the Dark Side of Addiction

The identification of a heuristic framework for the stages of the addiction cycle that are linked to neurocircuitry changes in pathophysiology includes the binge/intoxication stage, the withdrawal/negative affect stage, and the preoccupation/anticipation (craving) stage, which represent neuroadaptations in three neurocircuits (basal ganglia, extended amygdala, and frontal cortex, respectively). The identification of excellent and validated animal models, the development of human laboratory models, and an enormous surge in our understanding of neurocircuitry and neuropharmacological mechanisms have provided a revisionist view of addiction that emphasizes the loss of brain reward function and gain of stress function that drive negative reinforcement (the dark side of addiction) as a key to compulsive drug seeking. Reversing the dark side of addiction not only explains much of the existing successful pharmacotherapies for addiction but also points to vast new opportunities for future medications to alleviate this major source of human suffering.

Preclinical evidence implicating corticotropin-releasing factor signaling in ethanol consumption and neuroadaptation

The results of many studies support the influence of the corticotropin-releasing factor (CRF) system on ethanol (EtOH) consumption and EtOH-induced neuroadaptations that are critical in the addiction process. This review summarizes the preclinical data in this area after first providing an overview of the components of the CRF system. This complex system involves hypothalamic and extra-hypothalamic mechanisms that play a role in the central and peripheral consequences of stressors, including EtOH and other drugs of abuse. In addition, several endogenous ligands and targets make up this system and show differences in their involvement in EtOH drinking and in the effects of chronic or repeated EtOH treatment. In general, genetic and pharmacological approaches paint a consistent picture of the importance of CRF signaling via type 1 CRF receptors (CRF(1)) in EtOH-induced neuroadaptations that result in higher levels of intake, encourage alcohol seeking during abstinence and alter EtOH sensitivity. Furthermore, genetic findings in rodents, non-human primates and humans have provided some evidence of associations of genetic polymorphisms in CRF-related genes with EtOH drinking, although additional data are needed. These results suggest that CRF(1) antagonists have potential as pharmacotherapeutics for alcohol use disorders. However, given the broad and important role of these receptors in adaptation to environmental and other challenges, full antagonist effects may be too profound and consideration should be given to treatments with modulatory effects.

Brain pathways to recovery from alcohol dependence

This article highlights the research presentations at the satellite symposium on "Brain Pathways to Recovery from Alcohol Dependence" held at the 2013 Society for Neuroscience Annual Meeting. The purpose of this symposium was to provide an up to date overview of research efforts focusing on understanding brain mechanisms that contribute to recovery from alcohol dependence. A panel of scientists from the alcohol and addiction research field presented their insights and perspectives on brain mechanisms that may underlie both recovery and lack of recovery from alcohol dependence. The four sessions of the symposium encompassed multilevel studies exploring mechanisms underlying relapse and craving associated with sustained alcohol abstinence, cognitive function deficit and recovery, and translational studies on preventing relapse and promoting recovery. Gaps in our knowledge and research opportunities were also discussed.

Serotonergic Systems in the Pathophysiology of Ethanol Dependence: Relevance to Clinical Alcoholism

Alcoholism is a progressive brain disorder that is marked by increased sensitivity to the positive and negative reinforcing properties of ethanol, compulsive and habitual use despite negative consequences, and chronic relapse to alcohol drinking despite repeated attempts to reduce intake or abstain from alcohol. Emerging evidence from preclinical and clinical studies implicates serotonin (5-hydroxytryptamine; 5-HT) systems in the pathophysiology of alcohol dependence, suggesting that drugs targeting 5-HT systems may have utility in the treatment of alcohol use disorders. In this Review, we discuss the role of 5-HT systems in alcohol dependence with a focus on 5-HT interactions with neural circuits that govern all three stages of the addiction cycle. We attempt to clarify how 5-HT influences circuit function at these different stages with the goal of identifying neural targets for pharmacological treatment of this debilitating disorder.

The dark side of emotion: the addiction perspective

Emotions are "feeling" states and classic physiological emotive responses that are interpreted based on the history of the organism and the context. Motivation is a persistent state that leads to organized activity. Both are intervening variables and intimately related and have neural representations in the brain. The present thesis is that drugs of abuse elicit powerful emotions that can be interwoven conceptually into this framework. Such emotions range from pronounced euphoria to a devastating negative emotional state that in the extreme can create a break with homeostasis and thus an allostatic hedonic state that has been considered key to the etiology and maintenance of the pathophysiology of addiction. Drug addiction can be defined as a three-stage cycle-binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation-that involves allostatic changes in the brain reward and stress systems. Two primary sources of reinforcement, positive and negative reinforcement, have been hypothesized to play a role in this allostatic process. The negative emotional state that drives negative reinforcement is hypothesized to derive from dysregulation of key neurochemical elements involved in the brain incentive salience and stress systems. Specific neurochemical elements in these structures include not only decreases in incentive salience system function in the ventral striatum (within-system opponent processes) but also recruitment of the brain stress systems mediated by corticotropin-releasing factor (CRF), dynorphin-κ opioid systems, and norepinephrine, vasopressin, hypocretin, and substance P in the extended amygdala (between-system opponent processes). Neuropeptide Y, a powerful anti-stress neurotransmitter, has a profile of action on compulsive-like responding for drugs similar to a CRF1 receptor antagonist. Other stress buffers include nociceptin and endocannabinoids, which may also work through interactions with the extended amygdala. The thesis argued here is that the brain has specific neurochemical neurocircuitry coded by the hedonic extremes of pleasant and unpleasant emotions that have been identified through the study of opponent processes in the domain of addiction. These neurochemical systems need to be considered in the context of the framework that emotions involve the specific brain regions now identified to differentially interpreting emotive physiological expression.

Ethanol induced adaptations in 5-HT2c receptor signaling in the bed nucleus of the stria terminalis: implications for anxiety during ethanol withdrawal

One of the hallmarks of alcohol dependence is the presence of a withdrawal syndrome during abstinence, which manifests as physical craving for alcohol accompanied by subjective feelings of anxiety. Using a model of chronic intermittent ethanol (CIE) vapor in mice, we investigated the role of serotonin2c receptor (5HT2c-R) signaling in the BNST as a neural substrate underlying ethanol-induced anxiety during withdrawal. Mice were subjected to a 5-day CIE regimen of 16 h of ethanol vapor exposure followed by an 8 h "withdrawal" period between exposures. After the 5th and final exposure, mice were withdrawn for 24 h or 1 week before experiments began. Anxiety-like behavior was assessed in the social approach, light dark, and open field tests with mice showing deficits in social, but not general anxiety-like behavior that was alleviated by pretreatment with the 5HT2c-R antagonist SB 242,084 (3 mg/kg, i.p.) 24 h and 1 week post-CIE. Using immunohistochemistry and whole cell patch clamp electrophysiology, we also found that CIE increased FOS-IR and enhanced neuronal excitability in the ventral BNST (vBNST) 24 h into withdrawal in a 5HT2c-R dependent manner. This enhanced excitability persisted for 1 week post-CIE. We also found that mCPP, a 5HT2c/b agonist, induced a more robust depolarization in cells of the vBNST in CIE mice, confirming that 5HT2c-R signaling is upregulated in the vBNST following CIE. Taken together, these results suggest that CIE upregulates 5HT2c-R signaling in the vBNST, leading to increased excitability. This enhanced excitability of the vBNST may drive increased anxiety-like behavior during ethanol withdrawal.

Alcohol use disorders and current pharmacological therapies: the role of GABA(A) receptors

Alcohol use disorders (AUD) are defined as alcohol abuse and alcohol dependence, which create large problems both for society and for the drinkers themselves. To date, no therapeutic can effectively solve these problems. Understanding the underlying mechanisms leading to AUD is critically important for developing effective and safe pharmacological therapies. Benzodiazepines (BZs) are used to reduce the symptoms of alcohol withdrawal syndrome. However, frequent use of BZs causes cross-tolerance, dependence, and cross-addiction to alcohol. The FDA-approved naltrexone and acamprosate have shown mixed results in clinical trials. Naltrexone is effective to treat alcohol dependence (decreased length and frequency of drinking bouts), but its severe side effects, including withdrawal symptoms, are difficult to overcome. Acamprosate showed efficacy for treating alcohol dependence in European trials, but two large US trials have failed to confirm the efficacy. Another FDA-approved medication, disulfiram, does not diminish craving, and it causes a peripheral neuropathy. Kudzu is the only natural medication mentioned by the National Institute on Alcohol Abuse and Alcoholism, but its mechanisms of action are not yet established. It has been recently shown that dihydromyricetin, a flavonoid purified from Hovenia, has unique effects on GABAA receptors and blocks ethanol intoxication and withdrawal in alcoholic animal models. In this article, we review the role of GABAA receptors in the treatment of AUD and currently available and potentially novel pharmacological agents.

Alcohol stress response dampening during imminent versus distal, uncertain threat

Research indicates that fear and anxiety are distinct processes with separable neurobiological substrates. Predictable versus unpredictable shock administration has been used to elicit fear versus anxiety, respectively. Recent research has demonstrated that alcohol may reduce anxiety but not fear. However, previous manipulations of predictability have varied both probability and temporal uncertainty of shock threat, leaving unresolved questions regarding which stimulus characteristics elicit anxiety and are sensitive to alcohol stress-response dampening (SRD). We developed a novel paradigm to closely parallel basic research in animals that systematically varied temporal uncertainty of threat while holding threat probability constant. Intoxicated (0.08% target blood alcohol concentration), placebo, and no-alcohol control participants viewed a series of visual threat cues. Certain cue duration (5 s) blocks were equivalent to predictable shock blocks eliciting fear in earlier research. Uncertain cue duration (5, 20, 50, or 80 s, intermixed) blocks introduced temporal uncertainty regarding impending shock to elicit anxiety. Startle potentiation relative to matched cue periods in no-shock blocks provided the primary measure of affective response. All threat cues produced robust startle potentiation. Alcohol reduced startle potentiation during the first 5 s of threat cue presentation in uncertain but not certain duration blocks. Alcohol also reduced startle potentiation at later times among longer uncertain duration cues, suggesting that alcohol SRD persisted. Trait negative emotionality and binge drinking status moderated alcohol SRD magnitude during uncertain threat. These translational findings corroborate previous reports regarding distinct substrates of fear versus anxiety and have implications for both alcoholism etiology and comorbidity with anxiety disorders.

Schizophrenia and alcohol dependence: diverse clinical effects of oxytocin and their evolutionary origins

Beginning in 1979 with the first report that central administration of oxytocin stimulates maternal behavior in virgin rats, decades of animal research and more recent human studies have demonstrated that oxytocin has many pro-social effects. These many findings suggest that oxytocin may be an effective treatment for social deficits that are hallmark features of disorders such as autism and schizophrenia. Effects in preclinical animal models also imply that oxytocin may be an efficacious pharmacotherapy in a wide range of psychiatric disorders including psychoses and addictions. To date, 3 small clinical trials found that daily intranasal oxytocin treatment for 2-8 weeks significantly reduced psychotic symptoms in schizophrenia. Two of these trials also found improvement in social cognition or neurocognition, areas in which patients have significant deficiencies that do not respond to conventional antipsychotic treatment and contribute to disability. In another small trial, intranasal oxytocin potently blocked alcohol withdrawal. After reviewing the rationale for these trials, they are described in more detail. Questions are then asked followed by discussions of the large gaps in our knowledge about brain oxytocin systems in humans. The hope is to highlight important directions for future investigations of the role of oxytocin in the pathophysiology of psychotic disorders and addictions and to extend clinical research in these areas. Heretofore unrecognized roles for which oxytocin may have been selected during the evolution of placental mammalian maternal-infant and other social attachments are considered as possible origins of oxytocin antipsychotic and antiaddiction effects.This article is part of a Special Issue entitled Oxytocin and Social Behav.

Addiction as a stress surfeit disorder

Drug addiction has been conceptualized as a chronically relapsing disorder of compulsive drug seeking and taking that progresses through three stages: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. Drug addiction impacts multiple motivational mechanisms and can be conceptualized as a disorder that progresses from positive reinforcement (binge/intoxication stage) to negative reinforcement (withdrawal/negative affect stage). The construct of negative reinforcement is defined as drug taking that alleviates a negative emotional state. Our hypothesis is that the negative emotional state that drives such negative reinforcement is derived from dysregulation of key neurochemical elements involved in the brain stress systems within the frontal cortex, ventral striatum, and extended amygdala. Specific neurochemical elements in these structures include not only recruitment of the classic stress axis mediated by corticotropin-releasing factor (CRF) in the extended amygdala as previously hypothesized but also recruitment of dynorphin-κ opioid aversive systems in the ventral striatum and extended amygdala. Additionally, we hypothesized that these brain stress systems may be engaged in the frontal cortex early in the addiction process. Excessive drug taking engages activation of CRF not only in the extended amygdala, accompanied by anxiety-like states, but also in the medial prefrontal cortex, accompanied by deficits in executive function that may facilitate the transition to compulsive-like responding. Excessive activation of the nucleus accumbens via the release of mesocorticolimbic dopamine or activation of opioid receptors has long been hypothesized to subsequently activate the dynorphin-κ opioid system, which in turn can decrease dopaminergic activity in the mesocorticolimbic dopamine system. Blockade of the κ opioid system can also block anxiety-like and reward deficits associated with withdrawal from drugs of abuse and block the development of compulsive-like responding during extended access to drugs of abuse, suggesting another powerful brain stress/anti-reward system that contributes to compulsive drug seeking. Thus, brain stress response systems are hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the development and persistence of addiction. The recruitment of anti-reward systems provides a powerful neurochemical basis for the negative emotional states that are responsible for the dark side of addiction. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Addiction is a Reward Deficit and Stress Surfeit Disorder

Drug addiction can be defined by a three-stage cycle - binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation - that involves allostatic changes in the brain reward and stress systems. Two primary sources of reinforcement, positive and negative reinforcement, have been hypothesized to play a role in this allostatic process. The negative emotional state that drives negative reinforcement is hypothesized to derive from dysregulation of key neurochemical elements involved in the brain reward and stress systems. Specific neurochemical elements in these structures include not only decreases in reward system function (within-system opponent processes) but also recruitment of the brain stress systems mediated by corticotropin-releasing factor (CRF) and dynorphin-κ opioid systems in the ventral striatum, extended amygdala, and frontal cortex (both between-system opponent processes). CRF antagonists block anxiety-like responses associated with withdrawal, block increases in reward thresholds produced by withdrawal from drugs of abuse, and block compulsive-like drug taking during extended access. Excessive drug taking also engages the activation of CRF in the medial prefrontal cortex, paralleled by deficits in executive function that may facilitate the transition to compulsive-like responding. Neuropeptide Y, a powerful anti-stress neurotransmitter, has a profile of action on compulsive-like responding for ethanol similar to a CRF1 antagonist. Blockade of the κ opioid system can also block dysphoric-like effects associated with withdrawal from drugs of abuse and block the development of compulsive-like responding during extended access to drugs of abuse, suggesting another powerful brain stress system that contributes to compulsive drug seeking. The loss of reward function and recruitment of brain systems provide a powerful neurochemical basis that drives the compulsivity of addiction.

Transient increase in alcohol self-administration following a period of chronic exposure to corticosterone

Stressful life events and chronic stressors have been associated with escalations in alcohol drinking. Stress exposure leads to the secretion of glucocorticoids (cortisol in the human; corticosterone (CORT) in the rodent). To model a period of heightened elevations in CORT, the present work assessed the effects of chronic exposure to the stress hormone CORT on alcohol self-administration. Male Long Evans rats were trained to self-administer a sweetened alcohol solution (2% sucrose/15% alcohol) resulting in moderate levels of daily alcohol intake (0.5-0.7 g/kg). Following stable baseline operant self-administration, rats received CORT in the drinking water for 7 days. A transient increase in alcohol self-administration was observed on the first self-administration session following CORT exposure, and behavior returned to control levels by the second session. Control experiments determined that this increase in alcohol self-administration was specific to alcohol, unrelated to general motor activation, and functionally dissociated from decreased CORT levels at the time of testing. These results indicate that repeated exposure to heightened levels of stress hormone (e.g., as may be experienced during stressful episodes) has the potential to lead to exacerbated alcohol intake in low to moderate drinkers. Given that maladaptive drinking patterns, such as escalated alcohol drinking following stressful episodes, have the potential to put an individual at risk for future drinking disorders, utilization of this model will be important for examination of neuroadaptations that occur as a consequence of CORT exposure in order to better understand escalated drinking following stressful episodes in nondependent individuals.

Calorie restriction inhibits relapse behaviour and preference for alcohol within a two-bottle free choice paradigm in the alcohol preferring (iP) rat

Among its many beneficial effects, calorie restriction (CR) has also been found to reduce anxiety related behavior in the rodent. With heightened levels of stress and anxiety implicated as a key precipitating factor of relapse and alcohol addiction, it was found that a 25% CR in addition to inducing anxiolytic effects also had the capacity to reduce intake of alcohol and inhibit relapse within a model of operant self-administration. The aim of this study was to investigate if a 25% CR would also display similar effects in a two-bottle free choice paradigm, whereby 24 h ad libitum access to both 10% ethanol and water is provided. All animals were initially tested on the elevated plus maze (EPM) and open field test prior to commencing the two-bottle free choice paradigm. Differences between control and CR25% animals demonstrated the anxiolytic effects of CR, with the CR25% group displaying greater percentage of open arm/total arm duration and open arm/total arm entries in the EPM. During the acquisition phase of the two-bottle free choice paradigm, CR25% animals showed a reduced intake of 10% ethanol in ml/kg, in comparison to the control group. Whilst control animals displayed a strong preference for 10% ethanol, the CR25% group consumed both 10% ethanol and water equally with no differences found in total fluid intake between groups. Similarly this was also the case following forced deprivation. In addition to reduced intake and lack of preference for 10% ethanol, CR 25% animals unlike controls failed to display a typical alcohol deprivation effect following abstinence. Taken collectively the results of this study suggest that CR may act as a protective factor against addiction and relapse in the alcohol preferring (iP) rat. In addition, given CR25% animals did not display a preference for 10% ethanol, results also suggest that CR may be altering the hedonic impact of ethanol within this group.

Intranasal oxytocin blocks alcohol withdrawal in human subjects

BACKGROUND

The neuropeptide, oxytocin (OT), has been reported to block tolerance formation to alcohol and decrease withdrawal symptoms in alcohol-dependent rodents. Numerous recent studies in human subjects indicate that OT administered by the intranasal route penetrates into and exerts effects within the brain.

METHODS

In a randomized, double-blind clinical trial, intranasal OT (24 IU/dose, N = 7) or placebo (N = 4) was given twice daily for 3 days in alcohol-dependent subjects admitted to a research unit for medical detoxification using Clinical Institute Withdrawal Assessment for Alcohol (CIWA) score-driven PRN administration of lorazepam. Subjects rated themselves on the Alcohol Withdrawal Symptom Checklist (AWSC) each time CIWA scores were obtained. Subjects also completed the Penn Alcohol Craving Scale, an Alcohol Craving Visual Analog Scale (ACVAS) and the Profile of Mood States (POMS) on inpatient days 2 and 3.

RESULTS

All subjects had drunk heavily each day for at least 2 weeks prior to study and had previously experienced withdrawal upon stopping/decreasing alcohol consumption. OT was superior to placebo in reducing alcohol withdrawal as evidenced by: less total lorazepam required to complete detoxification (3.4 mg [4.7, SD] vs. 16.5 [4.4], p = 0.0015), lower mean CIWA scores on admission day 1 (4.3 [2.3] vs. 11.8 [0.4], p < 0.0001) and day 2 (3.4 [2.2] vs. 11.1 [3.6], p < 0.002), lower AWSC scores on days 1 and 2 (p < 0.02; p = 0.07), and lower ACVAS ratings (p = 0.01) and lower POMS Tension/Anxiety subscale scores on day 2 (p < 0.01).

CONCLUSIONS

This is the first demonstration that OT treatment may block alcohol withdrawal in human subjects. Our results are consistent with previous findings in rodents that OT inhibits neuroadaptation to and withdrawal from alcohol. OT could have advantages over benzodiazepines in managing alcohol withdrawal because it may reverse rather than maintain sedative-hypnotic tolerance. It will be important to test whether OT treatment is effective in reducing drinking in alcohol-dependent outpatients.

Alcohol stress response dampening: selective reduction of anxiety in the face of uncertain threat

Problematic alcohol use and stress response dampening (SRD) are intimately interconnected. Recent evidence suggests that alcohol produces selective SRD during uncertain but not certain threat. We systematically varied shock probability in a novel task assessing alcohol SRD during low probable/uncertain threat, while holding temporal precision of threat constant. Intoxicated (0.08% target blood alcohol concentration) and placebo participants completed a cued shock threat task in which probability of shock administration at the offset of brief visual cues varied parametrically. High probability (100%) shock cues represented certain threat as used in earlier research, while lower probability (20% and 60%) shock cues provided novel uncertain threat conditions. Startle potentiation during cues and inter-trial intervals (ITIs) served as the measure of affective response. General linear model analysis indicated that alcohol SRD magnitude increased monotonically as threat uncertainty increased. Alcohol SRD was significantly greater during 20% and 60% shock threat relative to 100% shock threat. Alcohol also significantly reduced startle potentiation during distal threat in shock-free ITIs. Alcohol SRD magnitude during distal/uncertain threat was meaningfully moderated by individual differences in negative affectivity and weekly alcohol consumption. This work advances understanding of which properties of uncertainty are relevant to anxiety and anxiolytic effects of alcohol.

Models of chronic alcohol exposure and dependence

Alcoholism is a chronic treatment-resistant disorder typically presenting with recurrent/cyclic periods of abusive drinking, withdrawal, abstinence, and relapse. Various strategies that attempt to model these processes in animals have been developed to elucidate the behavioral and neural processes underlying alcoholism. Many of these have involved chronic ethanol exposure and withdrawal with the most widely employed methods involving mice or rats. Prominent features of these methods include alcohol vapor or intragastric forced exposure, cyclic or intermittent periods of alcohol availability with various lengths of forced abstinence, voluntary consumption, the use of genetically alcohol-preferring animals, and inclusion of various pharmacological or environmental challenges to worsen or mitigate symptoms. This chapter emphasizes alcohol exposure and withdrawal and discusses representative metrics used to monitor the consequences of employing these methods. These include but are not limited to intensity and pattern of alcohol exposure, seizure sensitivity during withdrawal, and emotional responding.

Alcohol dose effects on stress response to cued threat vary by threat intensity

RATIONALE

Clarification of alcohol's effect on stress response during threat is critical to understand motivation for alcohol use and related alcohol-use disorders. Evaluation of stress response dampening (SRD) effects of alcohol has been limited by nonsystematic use of varied experimental methods and measures.

OBJECTIVES

This experiment parametrically varied alcohol dose and shock threat intensity among social drinkers to examine their effects on startle potentiation, a physiological measure of the affective component of the stress response.

METHODS

Ninety-six participants were assigned to one of four beverage groups: placebo and target blood alcohol concentration (BAC) groups of 0.04%, 0.075%, and 0.11%. Participants viewed colored cues presented in shock and no-shock blocks. Distinct colored cues predicted imminent low, moderate, or high intensity electric shock administration. Startle potentiation during shock threat relative to no-shock cues indexed affective response.

RESULTS

High threat increased startle potentiation relative to moderate/low intensity threat. Startle potentiation decreased as BAC increased. Threat intensity moderated this BAC effect with the strongest BAC effect observed during high threat. Analysis of individual difference moderators revealed reduced effect of BAC among heavier, more problematic drinkers.

CONCLUSIONS

Clear alcohol SRD effects were observed. These SRD effects were greatest at higher BACs and during more potent threat. Failure to account for these factors may partially explain inconsistent findings in past laboratory SRD research. Furthermore, they suggest greater reinforcement from alcohol at higher doses and among individuals with greater stress. Moderation of SRD effects by alcohol consumption and problems point to possible important risk factors.

Genetic propensities to increase ethanol intake in response to stress: studies with selectively bred swim test susceptible (SUS), alcohol-preferring (P), and non-preferring (NP) lines of rats

RATIONALE

Swim test susceptible (SUS) rats selectively bred for reduced struggling in the forced swim test (FST) following stress show high voluntary ethanol intake like alcohol-preferring (P) rats selectively bred for ethanol preference. It is unknown whether stress enhances drinking in SUS rats or FST behavior in P and non-preferring (NP) rats.

OBJECTIVES

The aim of this study was to assess the response to stress in male SUS, Sprague-Dawley (SD), P, and NP rats on 10% ethanol drinking and FST behavior.

METHODS

In experiment 1, SUS and SD rats had limited access to ethanol and water following white noise, rehousing, and forced swim stress. In experiment 2, P and NP rats received footshock, white noise, restraint, or no stress prior to the FST. Rats then had continuous access to ethanol and water, and the effects of weekly exposures to stress were measured.

RESULTS

SUS rats drank more ethanol (M = 2.98 g/kg) than SD rats (M = 1.26 g/kg) at baseline. Stress produced sustained increases (~33% of baseline) in ethanol intake in SUS rats. NP rats spent twice as much time immobile as P rats in the FST. Stress did not alter FST behavior in P or NP rats. Only footshock produced an increase (~29%) in ethanol intake in P rats.

CONCLUSIONS

Selection for stress-induced depressive-like behavior in SUS rats is associated with enhanced stress-induced ethanol drinking. However, the selection for alcohol preference is not associated with stress-induced depressive-like behavior but is associated with footshock stress-induced ethanol drinking. In these experiments, relationships among stress, depressive-like behavior, and alcohol preference were not symmetrical.

Effects of a stressor and corticotrophin releasing factor on ethanol deprivation-induced ethanol intake and anxiety-like behavior in alcohol-preferring P rats

RATIONALE

Stress may elevate ethanol drinking and anxiety associated with ethanol drinking. Studies to identify relevant neurobiological substrates are needed.

OBJECTIVE

To assess roles of brain regions in corticotrophin releasing factor (CRF) effects on stressor-enhanced, ethanol deprivation-induced drinking and anxiety-like behavior.

METHODS

Ethanol-preferring rats (P rats) were exposed to three cycles of a two-bottle choice paradigm with two 2-day deprivation periods that included 1 h exposure to a restraint stressor. To assess the role of CRF and to identify relevant brain regions, a CRF-1 receptor antagonist (SSR125543; 10 ug) was injected into the nucleus accumbens (NAC), amygdala (Amyg), or dorsal raphe nucleus (DRN) prior to exposure to the restraint stressor. In a second study, CRF (0.5 ug) was injected into one of these regions, or the ventral tegmental area (VTA), or paraventricular nucleus of the hypothalamus (PVN).

RESULTS

Applying the restraint stressor during deprivation increased voluntary intake and sensitized anxiety-like behavior. Antagonist injection into the NAC prevented increased drinking without affecting anxiety-like behavior, whereas injection into the Amyg or DRN prevented the anxiety-like behavior without affecting drinking. To confirm CRF actions in the stressor effect, CRF was injected into selected brain regions. NAC injections (but not the VTA, Amyg, DRN, or PVN) facilitated drinking but did not change anxiety-like behavior. Injections into the DRN or Amyg (but not PVN or VTA) enhanced anxiety-like behavior.

CONCLUSIONS

Results emphasize that a restraint stressor elevates ethanol intake and sensitizes ethanol deprivation-induced anxiety-like behavior through CRF1 receptors in the NAC and Amyg/DRN, respectively.

Chronic alcohol neuroadaptation and stress contribute to susceptibility for alcohol craving and relapse

Alcoholism is a chronic relapsing disorder. Major characteristics observed in alcoholics during an initial period of alcohol abstinence are altered physiological functions and a negative emotional state. Evidence suggests that a persistent, cumulative adaptation involving a kindling/allostasis-like process occurs during the course of repeated chronic alcohol exposures that is critical for the negative symptoms observed during alcohol withdrawal. Basic studies have provided evidence for specific neurotransmitters within identified brain sites being responsible for the negative emotion induced by the persistent cumulative adaptation following intermittent-alcohol exposures. After an extended period of abstinence, the cumulative alcohol adaptation increases susceptibility to stress- and alcohol cue-induced negative symptoms and alcohol seeking, both of which can facilitate excessive ingestion of alcohol. In the alcoholic, stressful imagery and alcohol cues alter physiological responses, enhance negative emotion, and induce craving. Brain fMRI imaging following stress and alcohol cues has documented neural changes in specific brain regions of alcoholics not observed in social drinkers. Such altered activity in brain of abstinent alcoholics to stress and alcohol cues is consistent with a continuing ethanol adaptation being responsible. Therapies in alcoholics found to block responses to stress and alcohol cues would presumably be potential treatments by which susceptibility for continued alcohol abuse can be reduced. By continuing to define the neurobiological basis of the sustained alcohol adaptation critical for the increased susceptibility of alcoholics to stress and alcohol cues that facilitate craving, a new era is expected to evolve in which the high rate of relapse in alcoholism is minimized.

Role of the serotonergic system in alcohol dependence: from animal models to clinics

Alcohol dependence remains among the most common substance abuse problems worldwide, and compulsive alcohol consumption is a significant public health concern. Alcohol is an addictive drug that alters brain function through interactions with multiple neurotransmitter systems. These neurotransmitter systems mediate the reinforcing effects of alcohol. Specifically, the serotonergic system is important in mediating alcohol reward, preference, dependence, and craving. In this review chapter, we first discuss the serotonin system as it relates to alcoholism, and then outline interactions between this system and other neurotransmitter systems. We emphasize the serotonin transporter and its possible role in alcoholism, then present several serotonergic receptors and discuss their contribution to alcoholism, and finally assess the serotonin system as a target for pharmacotherapy, with an emphasis on current and potential treatments.

Neuropeptide Y (NPY)-induced reductions in alcohol intake during continuous access and following alcohol deprivation are not altered by restraint stress in alcohol-preferring (P) rats

Administration of neuropeptide Y (NPY) reduces anxiety-like behavior and alcohol intake in alcohol-preferring rats. The present experiment examined whether the effects of NPY on alcohol drinking are modulated by stress exposure during continuous access or following ethanol deprivation. Female P rats underwent 6 weeks of continuous access to 15% v/v ethanol and water prior to intracerebroventricular (ICV) cannula implantation. Deprived rats underwent two cycles of 5 days of ethanol exposure followed by 2 days of ethanol deprivation, while non-deprived rats had uninterrupted access to ethanol. Stressed rats in both ethanol access groups were exposed to restraint stress for 1h 4-6h after ethanol was removed from the deprived group in both cycles. ICV infusions of 5.0 μg NPY or aCSF were administered 48 h following the deprivation/stress procedure, after which ethanol was returned. Rats showed increased ethanol intake following ethanol deprivation compared to non-deprived controls. Food and water intake were increased, while ethanol intake was decreased, in rats infused with NPY. Stress did not increase ethanol intake or alter the response to NPY. Although no stress effects were found, the present experiment replicates previous findings regarding the effectiveness of NPY in reducing ethanol consumption. Future studies aimed at determining the extent to which stress may affect relapse to ethanol drinking and response to NPY would benefit from implementing different stress paradigms and varying the pattern of ethanol access.

CRF-1 antagonist and CRF-2 agonist decrease binge-like ethanol drinking in C57BL/6J mice independent of the HPA axis

Recent evidence suggests that corticotropin-releasing factor (CRF) receptor (CRFR) signaling is involved in modulating binge-like ethanol consumption in C57BL/6J mice. In this report, a series of experiments were performed to further characterize the role of CRFR signaling in binge-like ethanol consumption. The role of central CRFR signaling was assessed with intracerebroventricular (i.c.v.) infusion of the nonselective CRFR antagonist, alpha-helical CRF(9-41) (0, 1, 5, 10 microg/1 microl). The contribution of central CRF type 2 receptor (CRF(2)R) signaling was assessed with i.c.v. infusion of the selective CRF(2)R agonist, urocortin (Ucn) 3 (0, 0.05, 0.1, or 0.5 microg/1 microl). The role of the hypothalamic-pituitary-adrenal (HPA) axis was assessed by pretreating mice with intraperitoneal (i.p.) injection of (1) the corticosterone synthesis inhibitor, metyrapone (0, 50, 100, 150 mg/kg) or (2) the glucocorticoid receptor antagonist, mifepristone (0, 25, 50 mg/kg), and (3) by using radioimmunoassay to determine whether binge-like ethanol intake influenced plasma corticosterone levels. Finally, we determined whether the ability of the CRF(1)R antagonist, CP-154,526 (CP; 0, 10, 15 mg/kg, i.p.), to blunt binge-like drinking required normal HPA axis signaling by comparing the effectiveness of CP in adrenalectomized (ADX) and normal mice. Results showed that i.c.v. infusion of a 1 microg dose of alpha-helical CRF(9-41) significantly attenuated binge-like ethanol consumption relative to vehicle treatment, and i.c.v. infusion of Ucn 3 dose-dependently blunted binge-like drinking. On the other hand, metyrapone nonselectively reduced both ethanol and sucrose consumption, mifepristone did not alter ethanol drinking, and binge-like drinking did not correlate with plasma corticosterone levels. Finally, i.p. injection of CP significantly attenuated binge-like ethanol intake in both ADX and normal mice. Together, these results suggest that binge-like ethanol intake in C57BL/6J mice is modulated by CRF(1)R and CRF(2)R signaling, such that blockade of CRF(1)R or activation of CRF(2)R effectively reduces excessive ethanol intake. Furthermore, normal HPA axis signaling is not necessary to achieve binge-like drinking behavior.

Genetic and environmental influences on ethanol consumption: perspectives from preclinical research

BACKGROUND

Alcohol use disorders (abuse and dependence, AUD) are multifactorial phenomena, depending on the interplay of environmental and genetic variables.

METHOD

This review describes current developments in animal research that may help (a) develop gene therapies for the treatment of alcoholism, (b) understand the permissive role of stress on ethanol intake, and (c) elucidate why exposure to ethanol early in life is associated with a greater risk of AUD.

RESULTS

The polymorphisms found in liver alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) affect the elimination of ethanol and the susceptibility to ethanol intake. A highly active ADH protects against alcoholism, an effect related to a presteady state burst in arterial acetaldehyde. Social stressors, such as repeated early maternal separation or social defeat, exert a permissive effect on ethanol intake, perhaps by altering the normal development of the hypothalamic-pituitary-adrenal axis. Ethanol exposure during gestation, infancy, or adolescence increases the likelihood of AUD later in life. Early perception of ethanol's positive and negative (anti-anxiety) reinforcing effects may play a role in this phenomenon.

CONCLUSIONS

The review underscores the advantages of using preclinical animal models of AUD and highlights points of intersection between the topics to help design a more integrated approach for the study of alcohol-related problems.

Corticotropin-releasing factor (CRF) sensitization of ethanol withdrawal-induced anxiety-like behavior is brain site specific and mediated by CRF-1 receptors: relation to stress-induced sensitization

In abstinent alcoholics, stress induces negative affect-a response linked to craving and relapse. In rats, repeated stresses at weekly intervals before 5-day ethanol diet sensitize withdrawal-induced anxiety-like behavior ("anxiety") that is blocked by a corticotrophin-releasing factor 1 (CRF-1)-receptor antagonist. Current experiments were performed to identify brain sites that support CRF involvement in stress sensitization of ethanol withdrawal-induced anxiety-like behavior. First, different doses of CRF microinjected weekly into the central amygdala (CeA) before ethanol exposure produced a dose-related sensitization of anxiety during ethanol withdrawal. Subsequently, CRF microinjection into the basolateral amygdala, dorsal raphe nucleus (DRN), or dorsal bed nucleus of the stria terminalis (d-BNST) also sensitized ethanol withdrawal-induced anxiety. In contrast, sensitization of ethanol withdrawal-induced anxiety was not observed after weekly CRF administration into the ventral-BNST, CA1-hippocampal region, or hypothalamic-paraventricular nucleus. Then, experiments documented the CRF receptor subtype responsible for CRF and stress sensitization of withdrawal-induced anxiety. Systemic administration of a CRF-1 receptor antagonist before CRF microinjection into the CeA, DRN, or d-BNST prevented CRF-induced sensitization of anxiety during ethanol withdrawal. Furthermore, repeated microinjections of urocortin-3, a CRF-2 receptor agonist, into the CRF-positive sites did not sensitize anxiety after withdrawal from ethanol. Finally, microinjection of a CRF-1 receptor antagonist into the CeA, DRN, or d-BNST before stress blocked sensitization of anxiety-like behavior induced by the repeated stress/ethanol withdrawal protocol. These results indicate that CRF released by stress acts on CRF-1 receptors within specific brain regions to produce a cumulative adaptation that sensitizes anxiety-like behavior during withdrawal from chronic ethanol exposure.

Effects of topiramate and other anti-glutamatergic drugs on the acute intoxicating actions of ethanol in mice: modulation by genetic strain and stress

Compounds with anti-glutamatergic properties currently in clinical use for various indications (eg Alzheimer's disease, epilepsy, psychosis, mood disorders) have potential utility as novel treatments for alcoholism. Enhanced sensitivity to certain acute intoxicating effects (ataxia, sedative) of alcohol may be one mechanism by which anti-glutamatergic drugs modulate alcohol use. We examined the effects of six compounds (memantine, dextromethorphan, haloperidol, lamotrigine, oxcarbazepine, and topiramate) on sensitivity to acute intoxicating effects of ethanol (ataxia, hypothermia, sedation/hypnosis) in C57BL/6J mice. Analysis of topiramate was extended to determine the influence of genetic background (by comparison of the 129S1, BALB/cJ, C57BL/6J, DBA/2J inbred strains) and prior stress history (by chronic exposure of C57BL/6J to swim stress) on topiramate's effects on ethanol-induced sedation/hypnosis. Results showed that one N-methyl-D-aspartate receptor (NMDAR) antagonist, memantine, but not another, dextromethorphan, potentiated the ataxic but not hypothermic or sedative/hypnotic effects of ethanol. Haloperidol increased ethanol-induced ataxia and sedation/hypnosis to a similar extent as the prototypical NMDAR antagonist MK-801. Of the anticonvulsants tested, lamotrigine accentuated ethanol-induced sedation/hypnosis, whereas oxcarbazepine was without effect. Topiramate was without effect per se under baseline conditions in C57BL/6J, but had a synergistic effect with MK-801 on ethanol-induced sedation/hypnosis. Comparing inbred strains, topiramate was found to significantly potentiate ethanol's sedative/hypnotic effects in BALB/cJ, but not 129S1, C57BL/6J, or DBA/2J strains. Topiramate also increased ethanol-induced sedation/hypnosis in C57BL/6J after exposure to chronic stress exposure. Current data demonstrate that with the exception of MK-801 and haloperidol, the compounds tested had either no significant or assay-selective effects on sensitivity to acute ethanol under baseline conditions in C57BL/6J. However, significant effects of topiramate were revealed as a function of co-treatment with an NMDAR blocker, genetic background, or prior stress history. These findings raise the possibility that topiramate and possibly other anti-glutamatergic drugs could promote the acute intoxicating effects of ethanol in specific subpopulations defined by genetics or life history.

Maternal separation stress in male mice: long-term increases in alcohol intake

RATIONALE

In rodents, prolonged maternal separation has been used as a model of developmentally early environmental stress to influence adult drug intake.

OBJECTIVES

The aim of the present study was to evaluate the long-term effects of prolonged maternal separation on alcohol consumption using two different self-administration procedures in mice: operant alcohol self-administration vs. three-bottle choice.

MATERIALS AND METHODS

From postnatal day (PND) 1 to 14, pups were separated from the dam (maternal separation, MS) daily for 180 min or were left undisturbed, only handled during cage cleaning (animal facility rearing, AFR). On PND 60, they were assigned to one of two experimental manipulations: either a three-bottle choice or operant oral alcohol self-administration. In the three-bottle choice procedure, mice were given access to 6% or 10% alcohol or 0.05% saccharin solution for 2 h/day for 10 days. In the second experiment, mice were reinforced for nose poking by delivery of oral alcohol (6% or 10% in saccharin) or 0.05% saccharin solutions during daily 30-min sessions. Following the acquisition phase, "break points" were determined. Later, mice were allowed 1 h access to the reinforcing solution with no dosage limitation.

RESULTS

In the three-bottle choice procedure, MS mice showed higher alcohol intake than AFR at the 10% alcohol concentration. In the operant alcohol self-administration, MS mice achieved higher alcohol intake than AFR at the concentrations 6% and 10% during the 1-h session.

CONCLUSIONS

The results demonstrate the long-term consequences of MS on alcohol intake in male mice, suggesting early life stress as a risk factor for alcohol consumption and abuse.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

The alcohol deprivation effect in C57BL/6J mice is observed using operant self-administration procedures and is modulated by CRF-1 receptor signaling

BACKGROUND

The alcohol deprivation effect (ADE) is characterized by transient excessive alcohol consumption upon reinstatement of ethanol following a period of ethanol deprivation. While this phenomenon has been observed in rats using both bottle drinking (consummatory behavior) and operant self-administration (consummatory and appetitive "ethanol-seeking" behavior) procedures, ADE studies in mice have primarily relied on bottle drinking measures. Furthermore, the neurochemical pathways that modulate the ADE are not well understood. Therefore, we determined whether the ADE can be observed in C57BL/6J mice using operant self-administration procedures and if expression of the ADE is modulated by the corticotropin releasing factor-1 (CRF-1) receptor.

METHODS

C57BL/6J mice were trained in a 2-hour operant self-administration paradigm to lever press for 10% ethanol or water on separate response keys. Between operant sessions, mice had access to ethanol in their homecage. Once stable responding occurred, mice were deprived of ethanol for 4 days and were then retested with ethanol in the operant paradigm for 3 consecutive days. Next, to assess the role of the CRF-1 receptor, mice were given intraperitoneal (i.p.) injection (0, 10, or 20 mg/kg) of the CRF-1 receptor antagonist CP-154,526 30 minutes before ADE testing. Additional experiments assessed (i) ADE responding in which the alternate response lever was inactive, (ii) the effects of CP-154,526 on self-administration of a 1% sucrose solution following 4 days of deprivation, and (iii) ADE responding in which mice did not received i.p. injections throughout the experiment.

RESULTS

Mice exhibited a significant increase in postdeprivation lever responding for ethanol with either a water reinforced or inactive alternate lever. Interestingly, i.p. injection of a 10 mg/kg dose of CP-154,526 protected against the ADE while not affecting lever responding for a sucrose solution. Finally, baseline and deprivation-induced increases of ethanol reinforced lever responding were greater in mice not given i.p. injections.

CONCLUSIONS

The ADE in C57BL/6J mice can be modeled using the operant self-administration paradigm and increased ethanol self-administration associated with the ADE is modulated by CRF-1 receptor signaling.

Effects of CRF1-receptor and opioid-receptor antagonists on dependence-induced increases in alcohol drinking by alcohol-preferring (P) rats

BACKGROUND

Selective breeding of rats over generations and induction of alcohol dependence via chronic vapor inhalation both enhance alcohol consumption in animal models. The purpose of this study was to determine whether dependence-induced increases in alcohol consumption by P rats is sensitive to naltrexone, a general opioid receptor antagonist (but with highest affinity at the mu-opioid receptor at low doses), and the recently characterized small molecule CRF(1)-receptor antagonist MPZP (N,N-bis(2-methoxyethyl)-3-(4-methoxy-2-methylphenyl)-2,5-dimethyl-pyrazolo[1,5-a]pyrimidin-7-amine).

METHODS

P rats (n = 20) were trained to respond for alcohol and water in a 2-lever operant situation during daily 30-minute sessions. P rats were then matched for alcohol intake and exposed to chronic intermittent alcohol vapor (n = 10) or ambient air (n = 10) for approximately 10 weeks. All rats were then administered MPZP and naltrexone in 2 separate and consecutive Latin-square designs.

RESULTS

MPZP attenuated dependence-induced increases in alcohol intake by P rats while having no effect on alcohol consumption by nondependent controls. Conversely, operant alcohol responding was reduced similarly in dependent and nondependent P rats by naltrexone.

CONCLUSIONS

These results confirm a role for brain CRF(1)-receptor systems in dependence-induced changes in the reinforcing properties of alcohol, and CRF(1)-receptor blockade appears to suppress dependence-induced drinking at lower doses in P rats relative to other rat lines. Therefore, brain CRF(1)-receptor systems are important in the regulation of dependence-induced alcohol consumption, whereas brain opioid systems are important in the regulation of basal alcohol consumption by rats.

Alcohol dependence, withdrawal, and relapse

Continued excessive alcohol consumption can lead to the development of dependence that is associated with a withdrawal syndrome when alcohol consumption is ceased or substantially reduced. This syndrome comprises physical signs as well as psychological symptoms that contribute to distress and psychological discomfort. For some people the fear of withdrawal symptoms may help perpetuate alcohol abuse; moreover, the presence of withdrawal symptoms may contribute to relapse after periods of abstinence. Withdrawal and relapse have been studied in both humans and animal models of alcoholism. Clinical studies demonstrated that alcohol-dependent people are more sensitive to relapse-provoking cues and stimuli than nondependent people, and similar observations have been made in animal models of alcohol dependence, withdrawal, and relapse. One factor contributing to relapse is withdrawal-related anxiety, which likely reflects adaptive changes in the brain in response to continued alcohol exposure. These changes affect, for example, the body's stress response system. The relationship between withdrawal, stress, and relapse also has implications for the treatment of alcoholic patients. Interestingly, animals with a history of alcohol dependence are more sensitive to certain medications that impact relapse-like behavior than animals without such a history, suggesting that it may be possible to develop medications that specifically target excessive, uncontrollable alcohol consumption.